mirror of
https://github.com/satwikkansal/wtfpython
synced 2024-11-22 11:04:25 +01:00
More changes to order and aesthetics
This commit is contained in:
parent
82c37ccb32
commit
28bcbfd311
188
README.md
vendored
188
README.md
vendored
@ -1303,7 +1303,7 @@ NameError: name 'e' is not defined
|
|||||||
|
|
||||||
* Source: https://docs.python.org/3/reference/compound_stmts.html#except
|
* Source: https://docs.python.org/3/reference/compound_stmts.html#except
|
||||||
|
|
||||||
When an exception has been assigned using `as` target, it is cleared at the end of the except clause. This is as if
|
When an exception has been assigned using `as` target, it is cleared at the end of the `except` clause. This is as if
|
||||||
|
|
||||||
```py
|
```py
|
||||||
except E as N:
|
except E as N:
|
||||||
@ -1378,8 +1378,75 @@ I've lost faith in truth!
|
|||||||
|
|
||||||
---
|
---
|
||||||
|
|
||||||
|
### ▶ Yielding from... return!
|
||||||
|
|
||||||
|
1\.
|
||||||
|
|
||||||
|
```py
|
||||||
|
def some_func(x):
|
||||||
|
if x == 3:
|
||||||
|
return ["wtf"]
|
||||||
|
else:
|
||||||
|
yield from range(x)
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output:**
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> list(some_func(3))
|
||||||
|
[]
|
||||||
|
```
|
||||||
|
|
||||||
|
Where did the `"wtf"` go? Is it due to some special effect of `yield from`? Let's validate that,
|
||||||
|
|
||||||
|
2\.
|
||||||
|
|
||||||
|
```py
|
||||||
|
def some_func(x):
|
||||||
|
if x == 3:
|
||||||
|
return ["wtf"]
|
||||||
|
else:
|
||||||
|
for i in range(x):
|
||||||
|
yield i
|
||||||
|
```
|
||||||
|
|
||||||
|
**Output (> 3.3):**
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> list(some_func(3))
|
||||||
|
[]
|
||||||
|
```
|
||||||
|
|
||||||
|
Same result, that didn't work either.
|
||||||
|
|
||||||
|
#### 💡 Explanation:
|
||||||
|
|
||||||
|
+ From Python 3.3 onwards, it became possible to use `return` statement with values inside generators (See [PEP380](https://www.python.org/dev/peps/pep-0380/)). The [official docs](https://www.python.org/dev/peps/pep-0380/#enhancements-to-stopiteration) say that,
|
||||||
|
|
||||||
|
> "... `return expr` in a generator causes `StopIteration(expr)` to be raised upon exit from the generator."
|
||||||
|
|
||||||
|
+ In case of `some_func(3)`, `StopIteration` is raised at the beginning because of `return` statement. The `StopIteration` exception is automatically catched inside the `list(...)` wrapper and the `for` loop. Therefore, the above two snippets result in an empty list.
|
||||||
|
|
||||||
|
+ To get `["wtf"]` from the generator `some_func` we need to catch the `StopIteration` exception,
|
||||||
|
|
||||||
|
```py
|
||||||
|
try:
|
||||||
|
next(some_func(3))
|
||||||
|
except StopIteration as e:
|
||||||
|
some_string = e.value
|
||||||
|
```
|
||||||
|
|
||||||
|
```py
|
||||||
|
>>> some_string
|
||||||
|
["wtf"]
|
||||||
|
```
|
||||||
|
|
||||||
|
---
|
||||||
|
|
||||||
### ▶ Lossy zip of iterators
|
### ▶ Lossy zip of iterators
|
||||||
|
|
||||||
<!-- Example ID: c28ed154-e59f-4070-8eb6-8967a4acac6d --->
|
<!-- Example ID: c28ed154-e59f-4070-8eb6-8967a4acac6d --->
|
||||||
|
|
||||||
```py
|
```py
|
||||||
>>> numbers = list(range(7))
|
>>> numbers = list(range(7))
|
||||||
>>> numbers
|
>>> numbers
|
||||||
@ -1407,8 +1474,7 @@ Where did element `3` go from the `numbers` list?
|
|||||||
result = []
|
result = []
|
||||||
for it in iterators:
|
for it in iterators:
|
||||||
elem = next(it, sentinel)
|
elem = next(it, sentinel)
|
||||||
if elem is sentinel:
|
if elem is sentinel: return
|
||||||
return
|
|
||||||
result.append(elem)
|
result.append(elem)
|
||||||
yield tuple(result)
|
yield tuple(result)
|
||||||
```
|
```
|
||||||
@ -1605,7 +1671,9 @@ The built-in `ord()` function returns a character's Unicode [code point](https:/
|
|||||||
---
|
---
|
||||||
|
|
||||||
### ▶ Teleportation
|
### ▶ Teleportation
|
||||||
|
|
||||||
<!-- Example ID: edafe923-0c20-4315-b6e1-0c31abfc38f5 --->
|
<!-- Example ID: edafe923-0c20-4315-b6e1-0c31abfc38f5 --->
|
||||||
|
|
||||||
```py
|
```py
|
||||||
import numpy as np
|
import numpy as np
|
||||||
|
|
||||||
@ -1858,8 +1926,8 @@ print(x, ': x in global')
|
|||||||
>>> x = 1
|
>>> x = 1
|
||||||
>>> print([x for x in range(5)])
|
>>> print([x for x in range(5)])
|
||||||
[0, 1, 2, 3, 4]
|
[0, 1, 2, 3, 4]
|
||||||
>>> print(x, ': x in global')
|
>>> print(x)
|
||||||
(4, ': x in global')
|
4
|
||||||
```
|
```
|
||||||
|
|
||||||
**Output (Python 3.x):**
|
**Output (Python 3.x):**
|
||||||
@ -1867,15 +1935,15 @@ print(x, ': x in global')
|
|||||||
>>> x = 1
|
>>> x = 1
|
||||||
>>> print([x for x in range(5)])
|
>>> print([x for x in range(5)])
|
||||||
[0, 1, 2, 3, 4]
|
[0, 1, 2, 3, 4]
|
||||||
>>> print(x, ': x in global')
|
>>> print(x)
|
||||||
1 : x in global
|
1
|
||||||
```
|
```
|
||||||
|
|
||||||
#### 💡 Explanation:
|
#### 💡 Explanation:
|
||||||
|
|
||||||
- In Python, for-loops use the scope they exist in and leave their defined loop-variable behind. This also applies if we explicitly defined the for-loop variable in the global namespace before. In this case, it will rebind the existing variable.
|
- In Python, for-loops use the scope they exist in and leave their defined loop-variable behind. This also applies if we explicitly defined the for-loop variable in the global namespace before. In this case, it will rebind the existing variable.
|
||||||
|
|
||||||
- The differences in the output of Python 2.x and Python 3.x interpreters for list comprehension example can be explained by following change documented in [What’s New In Python 3.0](https://docs.python.org/3/whatsnew/3.0.html) documentation:
|
- The differences in the output of Python 2.x and Python 3.x interpreters for list comprehension example can be explained by following change documented in [What’s New In Python 3.0](https://docs.python.org/3/whatsnew/3.0.html) change log:
|
||||||
|
|
||||||
> "List comprehensions no longer support the syntactic form `[... for var in item1, item2, ...]`. Use `[... for var in (item1, item2, ...)]` instead. Also, note that list comprehensions have different semantics: they are closer to syntactic sugar for a generator expression inside a `list()` constructor, and in particular the loop control variables are no longer leaked into the surrounding scope."
|
> "List comprehensions no longer support the syntactic form `[... for var in item1, item2, ...]`. Use `[... for var in (item1, item2, ...)]` instead. Also, note that list comprehensions have different semantics: they are closer to syntactic sugar for a generator expression inside a `list()` constructor, and in particular the loop control variables are no longer leaked into the surrounding scope."
|
||||||
|
|
||||||
@ -1883,6 +1951,7 @@ print(x, ': x in global')
|
|||||||
|
|
||||||
### ▶ Beware of default mutable arguments!
|
### ▶ Beware of default mutable arguments!
|
||||||
<!-- Example ID: 7d42dade-e20d-4a7b-9ed7-16fb58505fe9 --->
|
<!-- Example ID: 7d42dade-e20d-4a7b-9ed7-16fb58505fe9 --->
|
||||||
|
|
||||||
```py
|
```py
|
||||||
def some_func(default_arg=[]):
|
def some_func(default_arg=[]):
|
||||||
default_arg.append("some_string")
|
default_arg.append("some_string")
|
||||||
@ -2182,39 +2251,6 @@ class SomeClass:
|
|||||||
|
|
||||||
---
|
---
|
||||||
|
|
||||||
### ▶ From full to None in one instruction
|
|
||||||
|
|
||||||
<!-- Example ID: 9a0d5335-efe5-4eae-af44-584d15233066 --->
|
|
||||||
|
|
||||||
```py
|
|
||||||
some_list = [1, 2, 3]
|
|
||||||
some_dict = {
|
|
||||||
"key_1": 1,
|
|
||||||
"key_2": 2,
|
|
||||||
"key_3": 3
|
|
||||||
}
|
|
||||||
|
|
||||||
some_list = some_list.append(4)
|
|
||||||
some_dict = some_dict.update({"key_4": 4})
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> print(some_list)
|
|
||||||
None
|
|
||||||
>>> print(some_dict)
|
|
||||||
None
|
|
||||||
```
|
|
||||||
|
|
||||||
#### 💡 Explanation
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
|
|
||||||
|
|
||||||
### ▶ Needles in a Haystack
|
### ▶ Needles in a Haystack
|
||||||
|
|
||||||
<!-- Example ID: 52a199b1-989a-4b28-8910-dff562cebba9 --->
|
<!-- Example ID: 52a199b1-989a-4b28-8910-dff562cebba9 --->
|
||||||
@ -2235,6 +2271,7 @@ x, y = (0, 1) if True else None, None
|
|||||||
```
|
```
|
||||||
|
|
||||||
2\.
|
2\.
|
||||||
|
|
||||||
```py
|
```py
|
||||||
t = ('one', 'two')
|
t = ('one', 'two')
|
||||||
for i in t:
|
for i in t:
|
||||||
@ -2249,6 +2286,7 @@ print(t)
|
|||||||
```
|
```
|
||||||
|
|
||||||
**Output:**
|
**Output:**
|
||||||
|
|
||||||
```py
|
```py
|
||||||
one
|
one
|
||||||
two
|
two
|
||||||
@ -2288,7 +2326,9 @@ ten_words_list = [
|
|||||||
a = "python"
|
a = "python"
|
||||||
b = "javascript"
|
b = "javascript"
|
||||||
```
|
```
|
||||||
|
|
||||||
**Output:**
|
**Output:**
|
||||||
|
|
||||||
```py
|
```py
|
||||||
# An assert statement with an assertion failure message.
|
# An assert statement with an assertion failure message.
|
||||||
>>> assert(a == b, "Both languages are different")
|
>>> assert(a == b, "Both languages are different")
|
||||||
@ -2329,12 +2369,14 @@ None
|
|||||||
* `()` is a special token and denotes empty `tuple`.
|
* `()` is a special token and denotes empty `tuple`.
|
||||||
|
|
||||||
* In 3, as you might have already figured out, there's a missing comma after 5th element (`"that"`) in the list. So by implicit string literal concatenation,
|
* In 3, as you might have already figured out, there's a missing comma after 5th element (`"that"`) in the list. So by implicit string literal concatenation,
|
||||||
|
|
||||||
```py
|
```py
|
||||||
>>> ten_words_list
|
>>> ten_words_list
|
||||||
['some', 'very', 'big', 'list', 'thatconsists', 'of', 'exactly', 'ten', 'words']
|
['some', 'very', 'big', 'list', 'thatconsists', 'of', 'exactly', 'ten', 'words']
|
||||||
```
|
```
|
||||||
|
|
||||||
* No `AssertionError` was raised in 4th snippet because instead of asserting the individual expression `a == b`, we're asserting entire tuple. The following snippet will clear things up,
|
* No `AssertionError` was raised in 4th snippet because instead of asserting the individual expression `a == b`, we're asserting entire tuple. The following snippet will clear things up,
|
||||||
|
|
||||||
```py
|
```py
|
||||||
>>> a = "python"
|
>>> a = "python"
|
||||||
>>> b = "javascript"
|
>>> b = "javascript"
|
||||||
@ -2358,70 +2400,6 @@ None
|
|||||||
|
|
||||||
---
|
---
|
||||||
|
|
||||||
### ▶ Yielding from... return!
|
|
||||||
|
|
||||||
1\.
|
|
||||||
|
|
||||||
```py
|
|
||||||
def some_func(x):
|
|
||||||
if x == 3:
|
|
||||||
return ["wtf"]
|
|
||||||
else:
|
|
||||||
yield from range(x)
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output:**
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> list(some_func(3))
|
|
||||||
[]
|
|
||||||
```
|
|
||||||
|
|
||||||
Where did the `"wtf"` go? Is it due to some special effect of `yield from`? Let's validate that,
|
|
||||||
|
|
||||||
2\.
|
|
||||||
|
|
||||||
```py
|
|
||||||
def some_func(x):
|
|
||||||
if x == 3:
|
|
||||||
return ["wtf"]
|
|
||||||
else:
|
|
||||||
for i in range(x):
|
|
||||||
yield i
|
|
||||||
```
|
|
||||||
|
|
||||||
**Output (> 3.3):**
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> list(some_func(3))
|
|
||||||
[]
|
|
||||||
```
|
|
||||||
|
|
||||||
Same result, that didn't work either.
|
|
||||||
|
|
||||||
#### 💡 Explanation:
|
|
||||||
|
|
||||||
+ From Python 3.3 onwards, it became possible to use `return` statement with values inside generators (See [PEP380](https://www.python.org/dev/peps/pep-0380/)). The [official docs](https://www.python.org/dev/peps/pep-0380/#enhancements-to-stopiteration) say that,
|
|
||||||
|
|
||||||
> "... `return expr` in a generator causes `StopIteration(expr)` to be raised upon exit from the generator."
|
|
||||||
|
|
||||||
+ In case of `some_func(3)`, `StopIteration` is raised at the beginning because of `return` statement. The `StopIteration` exception is automatically catched inside the `list(...)` wrapper and the `for` loop. Therefore, the above two snippets result in an empty list.
|
|
||||||
|
|
||||||
+ To get `["wtf"]` from the generator `some_func` we need to catch the `StopIteration` exception,
|
|
||||||
```py
|
|
||||||
try:
|
|
||||||
next(some_func(3))
|
|
||||||
except StopIteration as e:
|
|
||||||
some_string = e.value
|
|
||||||
```
|
|
||||||
|
|
||||||
```py
|
|
||||||
>>> some_string
|
|
||||||
["wtf"]
|
|
||||||
```
|
|
||||||
|
|
||||||
---
|
|
||||||
|
|
||||||
### ▶ Wild imports
|
### ▶ Wild imports
|
||||||
<!-- Example ID: 83deb561-bd55-4461-bb5e-77dd7f411e1c --->
|
<!-- Example ID: 83deb561-bd55-4461-bb5e-77dd7f411e1c --->
|
||||||
```py
|
```py
|
||||||
|
Loading…
Reference in New Issue
Block a user