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coder9051 · web-flow · commit 270198d7628f · 2022-03-05T01:10:07.000+05:30
diff --git a/recursive_function (1).py b/recursive_function (1).py
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+# -*- coding: utf-8 -*-
+"""Recursive_function.ipynb
+
+Automatically generated by Colaboratory.
+
+Original file is located at
+    https://colab.research.google.com/drive/1bUQ87PdSkK5DRvQRoL94jEMcy5BizZi_
+
+**NOTE ON RECURSION**
+Recursive function:
+
+A recursive function calls itself. This mean that a new function is called from within the original function.
+
+
+For example look at the code below and assume a linked list counting from 0 to n by 1.
+"""
+
+def print_list(head):
+    if head is not None:
+        print(head.data)
+        print_list(head.next)
+
+"""The first function looks at the head of the list and prints it. It then creates a new function to print the next element. However,
+first function hasn't ended yet. It can't end until all the functions within it end. This is key to understanding.
+
+If we look at the call stack (the list of running functions) it looks like this:
+"""
+
+print_list() # the original outer most function, waiting for internal functions to end.
+    print_list() # the new function called within the original func.
+
+"""This just keeps on going. The new function calls another function. Now our stack looks like this:"""
+
+print_list() # the original function
+    print_list() # level 1 function.
+    	print_list() # level 2 function.
+
+"""The call stack keeps getting bigger and bigger because none of the outer functions can terminate because they are waiting on inner
+functions.
+"""
+
+print_list() # the original function
+    print_list() # level 1 function.
+    	print_list() # level 2 function.
+            ...
+                ...
+                    ...
+                        print_list() # level 1000 - Recursion depth hit. Program ends and error displayed.
+
+"""The call stack keeps getting bigger and bigger because none of the outer functions can terminate because they are waiting on inner
+functions.
+
+Recursion depth is a count of how many layers are active inside your recursive function. The default recursion depth limit for 
+Python 3 is 1000. The limit exists to prevent a stack overflow caused by too much (possibly infinite) recursion.
+
+Recursion is a cool tool and you should use it (or at least understand it). However, some languages have optimized tail call 
+recursion (what is the kind of recursion being shown above) and avoid this problem by ending the outer function when the inner one is called. Python has not.
+
+If you are writing a function that may hit the recursion limit it may be better to approach it iteratively (at least in Python).
+"""
