Added Python-Function-ID.md

For issue freeCodeCamp#819

Python-Function-ID.md

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+# Python id(object)
+
+`id()` is a built-in function in Python 3, which returns the *identity* of an object. The *identity* is a unique integer for that object during its lifetime. In CPython implementation, this is the address of the object in memory which is not necessarily true for other python implementations.
+
+## Argument
+
+### object
+
+The `object` argument can typically be a `int`,`float`, `str`,`list`, `dict`, `tuple` etc.
+
+## Return Value
+
+The return value would be a unique and constant `integer`.
+
+
+## Code Sample
+
+```python
+a = 2
+print(id(a)) #=> 140454723286976 (Values returned by id() might be different for different users)
+
+b = 3
+print(id(b)) #=> 140454723287008
+
+c = 2
+print(id(c)) #=> 140454723286976 (This is same as id(a) since they both contain the same value and hence have same memory address)
+
+print(id(a) == id(b)) #=> False (since a and b have different values stored in them)
+print(id(a) == id(c)) #=> True (since a and c have same values stored in them)
+
+d = 1.1
+e = 1.1 
+print(id(d) == id(e)) #=> True (since d and e have same values stored in them)
+
+str1 = 'hello'
+str2 = 'hello'
+print(id(str1) == id(str2)) #=> True (since str1 and str2 have same values stored in them)
+
+# For complex objects like lists, tuples, dictionaries etc. id() would give a unique integer even if the content of those containers is same.
+tup1 = (1,1)
+tup2 = (1,1)
+print(id(tup1) == id(tup2)) #=> False
+```
+
+:rocket: [REPL It!](https://repl.it/CQw7/1)
+
+[Official Docs](https://docs.python.org/3/library/functions.html#id)