From d1c8a538503278e9a1f417d5f3499d4dd6b8ca34 Mon Sep 17 00:00:00 2001
From: Satwik Kansal <satwikkansal@gmail.com>
Date: Sun, 27 Aug 2017 23:34:18 +0530
Subject: [PATCH] Add example- The function inside loop magic

---
 wtfpy.md | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/wtfpy.md b/wtfpy.md
index 64c40e8..5755d40 100755
--- a/wtfpy.md
+++ b/wtfpy.md
@@ -151,6 +151,57 @@ Quoting from https://docs.python.org/3/c-api/long.html
 ```
 
 
+## The loop magic
+
+```py
+funcs = []
+results = []
+for x in range(7):
+    def some_func():
+        return x
+    funcs.append(some_func)
+    results.append(some_func())
+
+funcs_results = [func() for func in funcs]
+```
+
+**Output:**
+```py
+>>> results
+[0, 1, 2, 3, 4, 5, 6]
+>>> funcs_results
+[6, 6, 6, 6, 6, 6, 6]
+```
+
+//OR
+
+```py
+>>> powers_of_x = [lambda x: x**i for i in range(10)]
+>>> [f(2) for f in powers_of_x]
+[512, 512, 512, 512, 512, 512, 512, 512, 512, 512]
+```
+
+### Explaination
+
+When defining a function inside a loop that uses the loop variable in its body, the loop function's closure is bound to the variable, not its value. So all of the functions use the latest value assigned to the variable for computation.
+
+To get the desired behavior you can pass in the loop variable as a named varibable to the function which will define the variable again within the function's scope.
+
+```py
+funcs = []
+for x in range(7):
+    def some_func(x=x):
+        return x
+    funcs.append(some_func)
+```
+
+**Output:**
+```py
+>>> funcs_results = [func() for func in funcs]
+>>> funcs_results
+[0, 1, 2, 3, 4, 5, 6]
+```
+
 # Contributing
 
 All patches are Welcome! Filing an issue first before submitting a patch will be appreciated :)