mirror of
https://github.com/satwikkansal/wtfpython
synced 2024-11-28 22:14:24 +01:00
Reorder the sections
This commit is contained in:
Satwik Kansal
parent
86462ed1e5
commit
98ef2dad4a
835
README.md
vendored
835
README.md
vendored
@ -26,67 +26,67 @@ So, here we go...
|
|||||||
- [Structure of the Examples](#structure-of-the-examples)
|
- [Structure of the Examples](#structure-of-the-examples)
|
||||||
- [Usage](#usage)
|
- [Usage](#usage)
|
||||||
- [👀 Examples](#-examples)
|
- [👀 Examples](#-examples)
|
||||||
- [Section: Appearances are deceptive!](#section-appearances-are-deceptive)
|
|
||||||
- [▶ Skipping lines?](#-skipping-lines)
|
|
||||||
- [▶ Teleportation *](#-teleportation-)
|
|
||||||
- [▶ Well, something is fishy...](#-well-something-is-fishy)
|
|
||||||
- [Section: The Hidden treasures!](#section-the-hidden-treasures)
|
|
||||||
- [▶ Okay Python, Can you make me fly? *](#-okay-python-can-you-make-me-fly-)
|
|
||||||
- [▶ `goto`, but why? *](#-goto-but-why-)
|
|
||||||
- [▶ Brace yourself! *](#-brace-yourself-)
|
|
||||||
- [▶ Let's meet Friendly Language Uncle For Life *](#-lets-meet-friendly-language-uncle-for-life-)
|
|
||||||
- [▶ Even Python understands that love is complicated *](#-even-python-understands-that-love-is-complicated-)
|
|
||||||
- [▶ Yes, it exists!](#-yes-it-exists)
|
|
||||||
- [▶ Inpinity *](#-inpinity-)
|
|
||||||
- [▶ Mangling time! *](#-mangling-time-)
|
|
||||||
- [Section: Strain your brain!](#section-strain-your-brain)
|
- [Section: Strain your brain!](#section-strain-your-brain)
|
||||||
- [▶ Strings can be tricky sometimes *](#-strings-can-be-tricky-sometimes-)
|
- [▶ Strings can be tricky sometimes *](#%E2%96%B6-strings-can-be-tricky-sometimes-)
|
||||||
- [▶ Time for some hash brownies!](#-time-for-some-hash-brownies)
|
- [▶ Time for some hash brownies!](#%E2%96%B6-time-for-some-hash-brownies)
|
||||||
- [▶ Return return everywhere!](#-return-return-everywhere)
|
- [▶ Return return everywhere!](#%E2%96%B6-return-return-everywhere)
|
||||||
- [▶ Deep down, we're all the same. *](#-deep-down-were-all-the-same-)
|
- [▶ Deep down, we're all the same. *](#%E2%96%B6-deep-down-were-all-the-same-)
|
||||||
- [▶ For what?](#-for-what)
|
- [▶ For what?](#%E2%96%B6-for-what)
|
||||||
- [▶ Evaluation time discrepancy](#-evaluation-time-discrepancy)
|
- [▶ Evaluation time discrepancy](#%E2%96%B6-evaluation-time-discrepancy)
|
||||||
- [▶ `is` is not what it is!](#-is-is-not-what-it-is)
|
- [▶ `is` is not what it is!](#%E2%96%B6-is-is-not-what-it-is)
|
||||||
- [▶ A tic-tac-toe where X wins in the first attempt!](#-a-tic-tac-toe-where-x-wins-in-the-first-attempt)
|
- [▶ A tic-tac-toe where X wins in the first attempt!](#%E2%96%B6-a-tic-tac-toe-where-x-wins-in-the-first-attempt)
|
||||||
- [▶ The sticky output function](#-the-sticky-output-function)
|
- [▶ The sticky output function](#%E2%96%B6-the-sticky-output-function)
|
||||||
- [▶ `is not ...` is not `is (not ...)`](#-is-not--is-not-is-not-)
|
- [▶ `is not ...` is not `is (not ...)`](#%E2%96%B6-is-not--is-not-is-not-)
|
||||||
- [▶ The surprising comma](#-the-surprising-comma)
|
- [▶ The surprising comma](#%E2%96%B6-the-surprising-comma)
|
||||||
- [▶ Backslashes at the end of string](#-backslashes-at-the-end-of-string)
|
- [▶ Backslashes at the end of string](#%E2%96%B6-backslashes-at-the-end-of-string)
|
||||||
- [▶ not knot!](#-not-knot)
|
- [▶ not knot!](#%E2%96%B6-not-knot)
|
||||||
- [▶ Half triple-quoted strings](#-half-triple-quoted-strings)
|
- [▶ Half triple-quoted strings](#%E2%96%B6-half-triple-quoted-strings)
|
||||||
- [▶ Midnight time doesn't exist?](#-midnight-time-doesnt-exist)
|
- [▶ Midnight time doesn't exist?](#%E2%96%B6-midnight-time-doesnt-exist)
|
||||||
- [▶ What's wrong with booleans?](#-whats-wrong-with-booleans)
|
- [▶ What's wrong with booleans?](#%E2%96%B6-whats-wrong-with-booleans)
|
||||||
- [▶ Class attributes and instance attributes](#-class-attributes-and-instance-attributes)
|
- [▶ Class attributes and instance attributes](#%E2%96%B6-class-attributes-and-instance-attributes)
|
||||||
- [▶ yielding None](#-yielding-none)
|
- [▶ yielding None](#%E2%96%B6-yielding-none)
|
||||||
- [▶ Mutating the immutable!](#-mutating-the-immutable)
|
- [▶ Mutating the immutable!](#%E2%96%B6-mutating-the-immutable)
|
||||||
- [▶ The disappearing variable from outer scope](#-the-disappearing-variable-from-outer-scope)
|
- [▶ The disappearing variable from outer scope](#%E2%96%B6-the-disappearing-variable-from-outer-scope)
|
||||||
- [▶ When True is actually False](#-when-true-is-actually-false)
|
- [▶ When True is actually False](#%E2%96%B6-when-true-is-actually-false)
|
||||||
- [▶ From filled to None in one instruction...](#-from-filled-to-none-in-one-instruction)
|
- [▶ From filled to None in one instruction...](#%E2%96%B6-from-filled-to-none-in-one-instruction)
|
||||||
- [▶ Subclass relationships *](#-subclass-relationships-)
|
- [▶ Subclass relationships *](#%E2%96%B6-subclass-relationships-)
|
||||||
- [▶ The mysterious key type conversion *](#-the-mysterious-key-type-conversion-)
|
- [▶ The mysterious key type conversion *](#%E2%96%B6-the-mysterious-key-type-conversion-)
|
||||||
- [▶ Let's see if you can guess this?](#-lets-see-if-you-can-guess-this)
|
- [▶ Let's see if you can guess this?](#%E2%96%B6-lets-see-if-you-can-guess-this)
|
||||||
|
- [Section: Appearances are deceptive!](#section-appearances-are-deceptive)
|
||||||
|
- [▶ Skipping lines?](#%E2%96%B6-skipping-lines)
|
||||||
|
- [▶ Teleportation *](#%E2%96%B6-teleportation-)
|
||||||
|
- [▶ Well, something is fishy...](#%E2%96%B6-well-something-is-fishy)
|
||||||
- [Section: Watch out for the landmines!](#section-watch-out-for-the-landmines)
|
- [Section: Watch out for the landmines!](#section-watch-out-for-the-landmines)
|
||||||
- [▶ Modifying a dictionary while iterating over it](#-modifying-a-dictionary-while-iterating-over-it)
|
- [▶ Modifying a dictionary while iterating over it](#%E2%96%B6-modifying-a-dictionary-while-iterating-over-it)
|
||||||
- [▶ Stubborn `del` operator *](#-stubborn-del-operator-)
|
- [▶ Stubborn `del` operator *](#%E2%96%B6-stubborn-del-operator-)
|
||||||
- [▶ Deleting a list item while iterating](#-deleting-a-list-item-while-iterating)
|
- [▶ Deleting a list item while iterating](#%E2%96%B6-deleting-a-list-item-while-iterating)
|
||||||
- [▶ Loop variables leaking out!](#-loop-variables-leaking-out)
|
- [▶ Loop variables leaking out!](#%E2%96%B6-loop-variables-leaking-out)
|
||||||
- [▶ Beware of default mutable arguments!](#-beware-of-default-mutable-arguments)
|
- [▶ Beware of default mutable arguments!](#%E2%96%B6-beware-of-default-mutable-arguments)
|
||||||
- [▶ Catching the Exceptions](#-catching-the-exceptions)
|
- [▶ Catching the Exceptions](#%E2%96%B6-catching-the-exceptions)
|
||||||
- [▶ Same operands, different story!](#-same-operands-different-story)
|
- [▶ Same operands, different story!](#%E2%96%B6-same-operands-different-story)
|
||||||
- [▶ The out of scope variable](#-the-out-of-scope-variable)
|
- [▶ The out of scope variable](#%E2%96%B6-the-out-of-scope-variable)
|
||||||
- [▶ Be careful with chained operations](#-be-careful-with-chained-operations)
|
- [▶ Be careful with chained operations](#%E2%96%B6-be-careful-with-chained-operations)
|
||||||
- [▶ Name resolution ignoring class scope](#-name-resolution-ignoring-class-scope)
|
- [▶ Name resolution ignoring class scope](#%E2%96%B6-name-resolution-ignoring-class-scope)
|
||||||
- [▶ Needle in a Haystack](#-needle-in-a-haystack)
|
- [▶ Needle in a Haystack](#%E2%96%B6-needle-in-a-haystack)
|
||||||
|
- [Section: The Hidden treasures!](#section-the-hidden-treasures)
|
||||||
|
- [▶ Okay Python, Can you make me fly? *](#%E2%96%B6-okay-python-can-you-make-me-fly-)
|
||||||
|
- [▶ `goto`, but why? *](#%E2%96%B6-goto-but-why-)
|
||||||
|
- [▶ Brace yourself! *](#%E2%96%B6-brace-yourself-)
|
||||||
|
- [▶ Let's meet Friendly Language Uncle For Life *](#%E2%96%B6-lets-meet-friendly-language-uncle-for-life-)
|
||||||
|
- [▶ Even Python understands that love is complicated *](#%E2%96%B6-even-python-understands-that-love-is-complicated-)
|
||||||
|
- [▶ Yes, it exists!](#%E2%96%B6-yes-it-exists)
|
||||||
|
- [▶ Inpinity *](#%E2%96%B6-inpinity-)
|
||||||
|
- [▶ Mangling time! *](#%E2%96%B6-mangling-time-)
|
||||||
- [Section: Miscallaneous](#section-miscallaneous)
|
- [Section: Miscallaneous](#section-miscallaneous)
|
||||||
- [▶ `+=` is faster](#--is-faster)
|
- [▶ `+=` is faster](#%E2%96%B6--is-faster)
|
||||||
- [▶ Let's make a giant string!](#-lets-make-a-giant-string)
|
- [▶ Let's make a giant string!](#%E2%96%B6-lets-make-a-giant-string)
|
||||||
- [▶ Explicit typecast of strings](#-explicit-typecast-of-strings)
|
- [▶ Explicit typecast of strings](#%E2%96%B6-explicit-typecast-of-strings)
|
||||||
- [▶ Minor Ones](#-minor-ones)
|
- [▶ Minor Ones](#%E2%96%B6-minor-ones)
|
||||||
- [Contributing](#contributing)
|
- [Contributing](#contributing)
|
||||||
- [Acknowledgements](#acknowledgements)
|
- [Acknowledgements](#acknowledgements)
|
||||||
- [🎓 License](#-license)
|
- [🎓 License](#-license)
|
||||||
- [Help](#help)
|
- [Help](#help)
|
||||||
- [Want to share WTFpython with friends?](#want-to-share-wtfpython-with-friends)
|
- [Want to share wtfpython with friends?](#want-to-share-wtfpython-with-friends)
|
||||||
- [Need a pdf version?](#need-a-pdf-version)
|
- [Need a pdf version?](#need-a-pdf-version)
|
||||||
|
|
||||||
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
|
<!-- END doctoc generated TOC please keep comment here to allow auto update -->
|
||||||
@ -153,371 +153,9 @@ Now, just run `wtfpython` at the command line which will open this collection in
|
|||||||
|
|
||||||
# 👀 Examples
|
# 👀 Examples
|
||||||
|
|
||||||
## Section: Appearances are deceptive!
|
|
||||||
|
|
||||||
This section is a gentle warm up before we focus on real Python concepts.
|
|
||||||
|
|
||||||
### ▶ Skipping lines?
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```py
|
|
||||||
>>> value = 11
|
|
||||||
>>> valuе = 32
|
|
||||||
>>> value
|
|
||||||
11
|
|
||||||
```
|
|
||||||
|
|
||||||
Wut?
|
|
||||||
|
|
||||||
**Note:** The easiest way to reproduce this is to simply copy the statements from the above snippet and paste them into your file/shell.
|
|
||||||
|
|
||||||
#### 💡 Explanation
|
|
||||||
|
|
||||||
Some non-Western characters look identical to letters in the English alphabet but are considered distinct by the interpreter.
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> ord('е') # cyrillic 'e' (Ye)
|
|
||||||
1077
|
|
||||||
>>> ord('e') # latin 'e', as used in English and typed using standard keyboard
|
|
||||||
101
|
|
||||||
>>> 'е' == 'e'
|
|
||||||
False
|
|
||||||
|
|
||||||
>>> value = 42 # latin e
|
|
||||||
>>> valuе = 23 # cyrillic 'e', Python 2.x interpreter would raise a `SyntaxError` here
|
|
||||||
>>> value
|
|
||||||
42
|
|
||||||
```
|
|
||||||
|
|
||||||
The built-in `ord()` function returns a character's Unicode [code point](https://en.wikipedia.org/wiki/Code_point), and different code positions of Cyrillic 'e' and Latin 'e' justify the behavior of the above example.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Teleportation *
|
|
||||||
|
|
||||||
```py
|
|
||||||
import numpy as np
|
|
||||||
|
|
||||||
def energy_send(x):
|
|
||||||
# Initializing a numpy array
|
|
||||||
np.array([float(x)])
|
|
||||||
|
|
||||||
def energy_receive():
|
|
||||||
# Return an empty numpy array
|
|
||||||
return np.empty((), dtype=np.float).tolist()
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```py
|
|
||||||
>>> energy_send(123.456)
|
|
||||||
>>> energy_receive()
|
|
||||||
123.456
|
|
||||||
```
|
|
||||||
|
|
||||||
Where's the Nobel Prize?
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
|
|
||||||
* Notice that the numpy array created in the `energy_send` function is not returned, so that memory space is free to reallocate.
|
|
||||||
* `numpy.empty()` returns the next free memory slot without reinitializing it. This memory spot just happens to be the same one that was just freed (usually, but not always).
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Well, something is fishy...
|
|
||||||
|
|
||||||
```py
|
|
||||||
def square(x):
|
|
||||||
"""
|
|
||||||
A simple function to calculate the square of a number by addition.
|
|
||||||
"""
|
|
||||||
sum_so_far = 0
|
|
||||||
for counter in range(x):
|
|
||||||
sum_so_far = sum_so_far + x
|
|
||||||
return sum_so_far
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output (Python 2.x):**
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> square(10)
|
|
||||||
10
|
|
||||||
```
|
|
||||||
|
|
||||||
Shouldn't that be 100?
|
|
||||||
|
|
||||||
**Note:** If you're not able to reproduce this, try running the file [mixed_tabs_and_spaces.py](/mixed_tabs_and_spaces.py) via the shell.
|
|
||||||
|
|
||||||
#### 💡 Explanation
|
|
||||||
|
|
||||||
* **Don't mix tabs and spaces!** The character just preceding return is a "tab", and the code is indented by multiple of "4 spaces" elsewhere in the example.
|
|
||||||
* This is how Python handles tabs:
|
|
||||||
> First, tabs are replaced (from left to right) by one to eight spaces such that the total number of characters up to and including the replacement is a multiple of eight <...>
|
|
||||||
* So the "tab" at the last line of `square` function is replaced with eight spaces, and it gets into the loop.
|
|
||||||
* Python 3 is kind enough to throw an error for such cases automatically.
|
|
||||||
|
|
||||||
**Output (Python 3.x):**
|
|
||||||
```py
|
|
||||||
TabError: inconsistent use of tabs and spaces in indentation
|
|
||||||
```
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
## Section: The Hidden treasures!
|
|
||||||
|
|
||||||
This section contains few of the lesser-known interesting things about Python that most beginners like me are unaware of (well, not anymore).
|
|
||||||
|
|
||||||
### ▶ Okay Python, Can you make me fly? *
|
|
||||||
|
|
||||||
Well, here you go
|
|
||||||
|
|
||||||
```py
|
|
||||||
import antigravity
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
Sshh.. It's a super secret.
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
+ `antigravity` module is one of the few easter eggs released by Python developers.
|
|
||||||
+ `import antigravity` opens up a web browser pointing to the [classic XKCD comic](http://xkcd.com/353/) about Python.
|
|
||||||
+ Well, there's more to it. There's **another easter egg inside the easter egg**. If look at the [code](https://github.com/python/cpython/blob/master/Lib/antigravity.py#L7-L17), there's a function defined that purports to implement the [XKCD's geohashing algorithm](https://xkcd.com/426/).
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ `goto`, but why? *
|
|
||||||
|
|
||||||
```py
|
|
||||||
from goto import goto, label
|
|
||||||
for i in range(9):
|
|
||||||
for j in range(9):
|
|
||||||
for k in range(9):
|
|
||||||
print("I'm trapped, please rescue!")
|
|
||||||
if k == 2:
|
|
||||||
goto .breakout # breaking out from a deeply nested loop
|
|
||||||
label .breakout
|
|
||||||
print("Freedom!")
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output (Python 2.3):**
|
|
||||||
```py
|
|
||||||
I'm trapped, please rescue!
|
|
||||||
I'm trapped, please rescue!
|
|
||||||
Freedom!
|
|
||||||
```
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
- A working version of `goto` in Python was [announced](https://mail.python.org/pipermail/python-announce-list/2004-April/002982.html) as an April Fool's joke on 1st April 2004.
|
|
||||||
- Current versions of Python do not have this module.
|
|
||||||
- Although it works, but please don't use it. Here's the [reason](https://docs.python.org/3/faq/design.html#why-is-there-no-goto) to why `goto` is not present in Python.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Brace yourself! *
|
|
||||||
|
|
||||||
If you are one of the people who doesn't like using whitespace in Python to denote scopes, you can use the C-style {} by importing,
|
|
||||||
|
|
||||||
```py
|
|
||||||
from __future__ import braces
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```py
|
|
||||||
File "some_file.py", line 1
|
|
||||||
from __future__ import braces
|
|
||||||
SyntaxError: not a chance
|
|
||||||
```
|
|
||||||
|
|
||||||
Braces? No way! If you think that's disappointing, use Java.
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
+ The `__future__` module is normally used to provide features from future versions of Python. The "future" here is however ironic.
|
|
||||||
+ This is an easter egg concerned with the community's feelings on this issue.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Let's meet Friendly Language Uncle For Life *
|
|
||||||
|
|
||||||
**Output (Python 3.x)**
|
|
||||||
```py
|
|
||||||
>>> from __future__ import barry_as_FLUFL
|
|
||||||
>>> "Ruby" != "Python" # there's no doubt about it
|
|
||||||
File "some_file.py", line 1
|
|
||||||
"Ruby" != "Python"
|
|
||||||
^
|
|
||||||
SyntaxError: invalid syntax
|
|
||||||
|
|
||||||
>>> "Ruby" <> "Python"
|
|
||||||
True
|
|
||||||
```
|
|
||||||
|
|
||||||
There we go.
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
- This is relevant to [PEP-401](https://www.python.org/dev/peps/pep-0401/) released on April 1, 2009 (now you know, what it means).
|
|
||||||
- Quoting from the PEP-401
|
|
||||||
> Recognized that the != inequality operator in Python 3.0 was a horrible, finger pain inducing mistake, the FLUFL reinstates the <> diamond operator as the sole spelling.
|
|
||||||
- There were more things that Uncle Barry had to share in the PEP; you can read them [here](https://www.python.org/dev/peps/pep-0401/).
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Even Python understands that love is complicated *
|
|
||||||
|
|
||||||
```py
|
|
||||||
import this
|
|
||||||
```
|
|
||||||
|
|
||||||
Wait, what's **this**? `this` is love :heart:
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```
|
|
||||||
The Zen of Python, by Tim Peters
|
|
||||||
|
|
||||||
Beautiful is better than ugly.
|
|
||||||
Explicit is better than implicit.
|
|
||||||
Simple is better than complex.
|
|
||||||
Complex is better than complicated.
|
|
||||||
Flat is better than nested.
|
|
||||||
Sparse is better than dense.
|
|
||||||
Readability counts.
|
|
||||||
Special cases aren't special enough to break the rules.
|
|
||||||
Although practicality beats purity.
|
|
||||||
Errors should never pass silently.
|
|
||||||
Unless explicitly silenced.
|
|
||||||
In the face of ambiguity, refuse the temptation to guess.
|
|
||||||
There should be one-- and preferably only one --obvious way to do it.
|
|
||||||
Although that way may not be obvious at first unless you're Dutch.
|
|
||||||
Now is better than never.
|
|
||||||
Although never is often better than *right* now.
|
|
||||||
If the implementation is hard to explain, it's a bad idea.
|
|
||||||
If the implementation is easy to explain, it may be a good idea.
|
|
||||||
Namespaces are one honking great idea -- let's do more of those!
|
|
||||||
```
|
|
||||||
|
|
||||||
It's the Zen of Python!
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> love = this
|
|
||||||
>>> this is love
|
|
||||||
True
|
|
||||||
>>> love is True
|
|
||||||
False
|
|
||||||
>>> love is False
|
|
||||||
False
|
|
||||||
>>> love is not True or False
|
|
||||||
True
|
|
||||||
>>> love is not True or False; love is love # Love is complicated
|
|
||||||
True
|
|
||||||
```
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
|
|
||||||
* `this` module in Python is an easter egg for The Zen Of Python ([PEP 20](https://www.python.org/dev/peps/pep-0020)).
|
|
||||||
* And if you think that's already interesting enough, check out the implementation of [this.py](https://hg.python.org/cpython/file/c3896275c0f6/Lib/this.py). Interestingly, the code for the Zen violates itself (and that's probably the only place where this happens).
|
|
||||||
* Regarding the statement `love is not True or False; love is love`, ironic but it's self-explanatory.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Yes, it exists!
|
|
||||||
|
|
||||||
**The `else` clause for loops.** One typical example might be:
|
|
||||||
|
|
||||||
```py
|
|
||||||
def does_exists_num(l, to_find):
|
|
||||||
for num in l:
|
|
||||||
if num == to_find:
|
|
||||||
print("Exists!")
|
|
||||||
break
|
|
||||||
else:
|
|
||||||
print("Does not exist")
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```py
|
|
||||||
>>> some_list = [1, 2, 3, 4, 5]
|
|
||||||
>>> does_exists_num(some_list, 4)
|
|
||||||
Exists!
|
|
||||||
>>> does_exists_num(some_list, -1)
|
|
||||||
Does not exist
|
|
||||||
```
|
|
||||||
|
|
||||||
**The `else` clause in exception handling.** An example,
|
|
||||||
|
|
||||||
```py
|
|
||||||
try:
|
|
||||||
pass
|
|
||||||
except:
|
|
||||||
print("Exception occurred!!!")
|
|
||||||
else:
|
|
||||||
print("Try block executed successfully...")
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```py
|
|
||||||
Try block executed successfully...
|
|
||||||
```
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
- The `else` clause after a loop is executed only when there's no explicit `break` after all the iterations.
|
|
||||||
- `else` clause after try block is also called "completion clause" as reaching the `else` clause in a `try` statement means that the try block actually completed successfully.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Inpinity *
|
|
||||||
|
|
||||||
The spelling is intended. Please, don't submit a patch for this.
|
|
||||||
|
|
||||||
**Output (Python 3.x):**
|
|
||||||
```py
|
|
||||||
>>> infinity = float('infinity')
|
|
||||||
>>> hash(infinity)
|
|
||||||
314159
|
|
||||||
>>> hash(float('-inf'))
|
|
||||||
-314159
|
|
||||||
```
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
- Hash of infinity is 10⁵ x π.
|
|
||||||
- Interestingly, the hash of `float('-inf')` is "-10⁵ x π" in Python 3, whereas "-10⁵ x e" in Python 2.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Mangling time! *
|
|
||||||
|
|
||||||
```py
|
|
||||||
class Yo(object):
|
|
||||||
def __init__(self):
|
|
||||||
self.__honey = True
|
|
||||||
self.bitch = True
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
```py
|
|
||||||
>>> Yo().bitch
|
|
||||||
True
|
|
||||||
>>> Yo().__honey
|
|
||||||
AttributeError: 'Yo' object has no attribute '__honey'
|
|
||||||
>>> Yo()._Yo__honey
|
|
||||||
True
|
|
||||||
```
|
|
||||||
|
|
||||||
Why did `Yo()._Yo__honey` worked? Only Indian readers would understand.
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
|
|
||||||
* [Name Mangling](https://en.wikipedia.org/wiki/Name_mangling) is used to avoid naming collisions between different namespaces.
|
|
||||||
* In Python, the interpreter modifies (mangles) the class member names starting with `__` (double underscore) and not ending with more than one trailing underscore by adding `_NameOfTheClass` in front.
|
|
||||||
* So, to access `__honey` attribute, we are required to append `_Yo` to the front which would prevent conflicts with the same name attribute defined in any other class.
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
## Section: Strain your brain!
|
## Section: Strain your brain!
|
||||||
|
|
||||||
Alright, it's time to strain your brain and test your understanding of Python concepts. All the best!
|
|
||||||
|
|
||||||
### ▶ Strings can be tricky sometimes *
|
### ▶ Strings can be tricky sometimes *
|
||||||
|
|
||||||
1\.
|
1\.
|
||||||
@ -1539,6 +1177,115 @@ a, b = a[b] = {}, 5
|
|||||||
|
|
||||||
---
|
---
|
||||||
|
|
||||||
|
## Section: Appearances are deceptive!
|
||||||
|
|
||||||
|
### ▶ Skipping lines?
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```py
|
||||||
|
>>> value = 11
|
||||||
|
>>> valuе = 32
|
||||||
|
>>> value
|
||||||
|
11
|
||||||
|
```
|
||||||
|
|
||||||
|
Wut?
|
||||||
|
|
||||||
|
**Note:** The easiest way to reproduce this is to simply copy the statements from the above snippet and paste them into your file/shell.
|
||||||
|
|
||||||
|
#### 💡 Explanation
|
||||||
|
|
||||||
|
Some non-Western characters look identical to letters in the English alphabet but are considered distinct by the interpreter.
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> ord('е') # cyrillic 'e' (Ye)
|
||||||
|
1077
|
||||||
|
>>> ord('e') # latin 'e', as used in English and typed using standard keyboard
|
||||||
|
101
|
||||||
|
>>> 'е' == 'e'
|
||||||
|
False
|
||||||
|
|
||||||
|
>>> value = 42 # latin e
|
||||||
|
>>> valuе = 23 # cyrillic 'e', Python 2.x interpreter would raise a `SyntaxError` here
|
||||||
|
>>> value
|
||||||
|
42
|
||||||
|
```
|
||||||
|
|
||||||
|
The built-in `ord()` function returns a character's Unicode [code point](https://en.wikipedia.org/wiki/Code_point), and different code positions of Cyrillic 'e' and Latin 'e' justify the behavior of the above example.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Teleportation *
|
||||||
|
|
||||||
|
```py
|
||||||
|
import numpy as np
|
||||||
|
|
||||||
|
def energy_send(x):
|
||||||
|
# Initializing a numpy array
|
||||||
|
np.array([float(x)])
|
||||||
|
|
||||||
|
def energy_receive():
|
||||||
|
# Return an empty numpy array
|
||||||
|
return np.empty((), dtype=np.float).tolist()
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```py
|
||||||
|
>>> energy_send(123.456)
|
||||||
|
>>> energy_receive()
|
||||||
|
123.456
|
||||||
|
```
|
||||||
|
|
||||||
|
Where's the Nobel Prize?
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
|
||||||
|
* Notice that the numpy array created in the `energy_send` function is not returned, so that memory space is free to reallocate.
|
||||||
|
* `numpy.empty()` returns the next free memory slot without reinitializing it. This memory spot just happens to be the same one that was just freed (usually, but not always).
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Well, something is fishy...
|
||||||
|
|
||||||
|
```py
|
||||||
|
def square(x):
|
||||||
|
"""
|
||||||
|
A simple function to calculate the square of a number by addition.
|
||||||
|
"""
|
||||||
|
sum_so_far = 0
|
||||||
|
for counter in range(x):
|
||||||
|
sum_so_far = sum_so_far + x
|
||||||
|
return sum_so_far
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output (Python 2.x):**
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> square(10)
|
||||||
|
10
|
||||||
|
```
|
||||||
|
|
||||||
|
Shouldn't that be 100?
|
||||||
|
|
||||||
|
**Note:** If you're not able to reproduce this, try running the file [mixed_tabs_and_spaces.py](/mixed_tabs_and_spaces.py) via the shell.
|
||||||
|
|
||||||
|
#### 💡 Explanation
|
||||||
|
|
||||||
|
* **Don't mix tabs and spaces!** The character just preceding return is a "tab", and the code is indented by multiple of "4 spaces" elsewhere in the example.
|
||||||
|
* This is how Python handles tabs:
|
||||||
|
> First, tabs are replaced (from left to right) by one to eight spaces such that the total number of characters up to and including the replacement is a multiple of eight <...>
|
||||||
|
* So the "tab" at the last line of `square` function is replaced with eight spaces, and it gets into the loop.
|
||||||
|
* Python 3 is kind enough to throw an error for such cases automatically.
|
||||||
|
|
||||||
|
**Output (Python 3.x):**
|
||||||
|
```py
|
||||||
|
TabError: inconsistent use of tabs and spaces in indentation
|
||||||
|
```
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
## Section: Watch out for the landmines!
|
## Section: Watch out for the landmines!
|
||||||
|
|
||||||
|
|
||||||
@ -2091,6 +1838,257 @@ tuple()
|
|||||||
|
|
||||||
---
|
---
|
||||||
|
|
||||||
|
|
||||||
|
## Section: The Hidden treasures!
|
||||||
|
|
||||||
|
This section contains few of the lesser-known interesting things about Python that most beginners like me are unaware of (well, not anymore).
|
||||||
|
|
||||||
|
### ▶ Okay Python, Can you make me fly? *
|
||||||
|
|
||||||
|
Well, here you go
|
||||||
|
|
||||||
|
```py
|
||||||
|
import antigravity
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
Sshh.. It's a super secret.
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
+ `antigravity` module is one of the few easter eggs released by Python developers.
|
||||||
|
+ `import antigravity` opens up a web browser pointing to the [classic XKCD comic](http://xkcd.com/353/) about Python.
|
||||||
|
+ Well, there's more to it. There's **another easter egg inside the easter egg**. If look at the [code](https://github.com/python/cpython/blob/master/Lib/antigravity.py#L7-L17), there's a function defined that purports to implement the [XKCD's geohashing algorithm](https://xkcd.com/426/).
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ `goto`, but why? *
|
||||||
|
|
||||||
|
```py
|
||||||
|
from goto import goto, label
|
||||||
|
for i in range(9):
|
||||||
|
for j in range(9):
|
||||||
|
for k in range(9):
|
||||||
|
print("I'm trapped, please rescue!")
|
||||||
|
if k == 2:
|
||||||
|
goto .breakout # breaking out from a deeply nested loop
|
||||||
|
label .breakout
|
||||||
|
print("Freedom!")
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output (Python 2.3):**
|
||||||
|
```py
|
||||||
|
I'm trapped, please rescue!
|
||||||
|
I'm trapped, please rescue!
|
||||||
|
Freedom!
|
||||||
|
```
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
- A working version of `goto` in Python was [announced](https://mail.python.org/pipermail/python-announce-list/2004-April/002982.html) as an April Fool's joke on 1st April 2004.
|
||||||
|
- Current versions of Python do not have this module.
|
||||||
|
- Although it works, but please don't use it. Here's the [reason](https://docs.python.org/3/faq/design.html#why-is-there-no-goto) to why `goto` is not present in Python.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Brace yourself! *
|
||||||
|
|
||||||
|
If you are one of the people who doesn't like using whitespace in Python to denote scopes, you can use the C-style {} by importing,
|
||||||
|
|
||||||
|
```py
|
||||||
|
from __future__ import braces
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```py
|
||||||
|
File "some_file.py", line 1
|
||||||
|
from __future__ import braces
|
||||||
|
SyntaxError: not a chance
|
||||||
|
```
|
||||||
|
|
||||||
|
Braces? No way! If you think that's disappointing, use Java.
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
+ The `__future__` module is normally used to provide features from future versions of Python. The "future" here is however ironic.
|
||||||
|
+ This is an easter egg concerned with the community's feelings on this issue.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Let's meet Friendly Language Uncle For Life *
|
||||||
|
|
||||||
|
**Output (Python 3.x)**
|
||||||
|
```py
|
||||||
|
>>> from __future__ import barry_as_FLUFL
|
||||||
|
>>> "Ruby" != "Python" # there's no doubt about it
|
||||||
|
File "some_file.py", line 1
|
||||||
|
"Ruby" != "Python"
|
||||||
|
^
|
||||||
|
SyntaxError: invalid syntax
|
||||||
|
|
||||||
|
>>> "Ruby" <> "Python"
|
||||||
|
True
|
||||||
|
```
|
||||||
|
|
||||||
|
There we go.
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
- This is relevant to [PEP-401](https://www.python.org/dev/peps/pep-0401/) released on April 1, 2009 (now you know, what it means).
|
||||||
|
- Quoting from the PEP-401
|
||||||
|
> Recognized that the != inequality operator in Python 3.0 was a horrible, finger pain inducing mistake, the FLUFL reinstates the <> diamond operator as the sole spelling.
|
||||||
|
- There were more things that Uncle Barry had to share in the PEP; you can read them [here](https://www.python.org/dev/peps/pep-0401/).
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Even Python understands that love is complicated *
|
||||||
|
|
||||||
|
```py
|
||||||
|
import this
|
||||||
|
```
|
||||||
|
|
||||||
|
Wait, what's **this**? `this` is love :heart:
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```
|
||||||
|
The Zen of Python, by Tim Peters
|
||||||
|
|
||||||
|
Beautiful is better than ugly.
|
||||||
|
Explicit is better than implicit.
|
||||||
|
Simple is better than complex.
|
||||||
|
Complex is better than complicated.
|
||||||
|
Flat is better than nested.
|
||||||
|
Sparse is better than dense.
|
||||||
|
Readability counts.
|
||||||
|
Special cases aren't special enough to break the rules.
|
||||||
|
Although practicality beats purity.
|
||||||
|
Errors should never pass silently.
|
||||||
|
Unless explicitly silenced.
|
||||||
|
In the face of ambiguity, refuse the temptation to guess.
|
||||||
|
There should be one-- and preferably only one --obvious way to do it.
|
||||||
|
Although that way may not be obvious at first unless you're Dutch.
|
||||||
|
Now is better than never.
|
||||||
|
Although never is often better than *right* now.
|
||||||
|
If the implementation is hard to explain, it's a bad idea.
|
||||||
|
If the implementation is easy to explain, it may be a good idea.
|
||||||
|
Namespaces are one honking great idea -- let's do more of those!
|
||||||
|
```
|
||||||
|
|
||||||
|
It's the Zen of Python!
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> love = this
|
||||||
|
>>> this is love
|
||||||
|
True
|
||||||
|
>>> love is True
|
||||||
|
False
|
||||||
|
>>> love is False
|
||||||
|
False
|
||||||
|
>>> love is not True or False
|
||||||
|
True
|
||||||
|
>>> love is not True or False; love is love # Love is complicated
|
||||||
|
True
|
||||||
|
```
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
|
||||||
|
* `this` module in Python is an easter egg for The Zen Of Python ([PEP 20](https://www.python.org/dev/peps/pep-0020)).
|
||||||
|
* And if you think that's already interesting enough, check out the implementation of [this.py](https://hg.python.org/cpython/file/c3896275c0f6/Lib/this.py). Interestingly, the code for the Zen violates itself (and that's probably the only place where this happens).
|
||||||
|
* Regarding the statement `love is not True or False; love is love`, ironic but it's self-explanatory.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Yes, it exists!
|
||||||
|
|
||||||
|
**The `else` clause for loops.** One typical example might be:
|
||||||
|
|
||||||
|
```py
|
||||||
|
def does_exists_num(l, to_find):
|
||||||
|
for num in l:
|
||||||
|
if num == to_find:
|
||||||
|
print("Exists!")
|
||||||
|
break
|
||||||
|
else:
|
||||||
|
print("Does not exist")
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```py
|
||||||
|
>>> some_list = [1, 2, 3, 4, 5]
|
||||||
|
>>> does_exists_num(some_list, 4)
|
||||||
|
Exists!
|
||||||
|
>>> does_exists_num(some_list, -1)
|
||||||
|
Does not exist
|
||||||
|
```
|
||||||
|
|
||||||
|
**The `else` clause in exception handling.** An example,
|
||||||
|
|
||||||
|
```py
|
||||||
|
try:
|
||||||
|
pass
|
||||||
|
except:
|
||||||
|
print("Exception occurred!!!")
|
||||||
|
else:
|
||||||
|
print("Try block executed successfully...")
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```py
|
||||||
|
Try block executed successfully...
|
||||||
|
```
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
- The `else` clause after a loop is executed only when there's no explicit `break` after all the iterations.
|
||||||
|
- `else` clause after try block is also called "completion clause" as reaching the `else` clause in a `try` statement means that the try block actually completed successfully.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Inpinity *
|
||||||
|
|
||||||
|
The spelling is intended. Please, don't submit a patch for this.
|
||||||
|
|
||||||
|
**Output (Python 3.x):**
|
||||||
|
```py
|
||||||
|
>>> infinity = float('infinity')
|
||||||
|
>>> hash(infinity)
|
||||||
|
314159
|
||||||
|
>>> hash(float('-inf'))
|
||||||
|
-314159
|
||||||
|
```
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
- Hash of infinity is 10⁵ x π.
|
||||||
|
- Interestingly, the hash of `float('-inf')` is "-10⁵ x π" in Python 3, whereas "-10⁵ x e" in Python 2.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
### ▶ Mangling time! *
|
||||||
|
|
||||||
|
```py
|
||||||
|
class Yo(object):
|
||||||
|
def __init__(self):
|
||||||
|
self.__honey = True
|
||||||
|
self.bitch = True
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
```py
|
||||||
|
>>> Yo().bitch
|
||||||
|
True
|
||||||
|
>>> Yo().__honey
|
||||||
|
AttributeError: 'Yo' object has no attribute '__honey'
|
||||||
|
>>> Yo()._Yo__honey
|
||||||
|
True
|
||||||
|
```
|
||||||
|
|
||||||
|
Why did `Yo()._Yo__honey` worked? Only Indian readers would understand.
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
|
||||||
|
* [Name Mangling](https://en.wikipedia.org/wiki/Name_mangling) is used to avoid naming collisions between different namespaces.
|
||||||
|
* In Python, the interpreter modifies (mangles) the class member names starting with `__` (double underscore) and not ending with more than one trailing underscore by adding `_NameOfTheClass` in front.
|
||||||
|
* So, to access `__honey` attribute, we are required to append `_Yo` to the front which would prevent conflicts with the same name attribute defined in any other class.
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
## Section: Miscallaneous
|
## Section: Miscallaneous
|
||||||
|
|
||||||
|
|
||||||
@ -2324,6 +2322,9 @@ The idea and design for this collection were initially inspired by Denys Dovhan'
|
|||||||
[license-url]: http://www.wtfpl.net
|
[license-url]: http://www.wtfpl.net
|
||||||
[license-image]: https://img.shields.io/badge/License-WTFPL%202.0-lightgrey.svg?style=flat-square
|
[license-image]: https://img.shields.io/badge/License-WTFPL%202.0-lightgrey.svg?style=flat-square
|
||||||
|
|
||||||
|
## Help
|
||||||
|
|
||||||
|
If you have any wtfs, ideas or suggestions, please share.
|
||||||
|
|
||||||
## Want to share wtfpython with friends?
|
## Want to share wtfpython with friends?
|
||||||
|
|
||||||
|
|||||||
Loading…
Reference in New Issue
Block a user