Create using_an_unpythonic_loop.rst.

kaycebasques · kaycebasques · commit e801fd81b3f9 · 2014-10-02T21:51:50.000-07:00
diff --git a/docs/correctness/using_an_unpythonic_loop.rst b/docs/correctness/using_an_unpythonic_loop.rst
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+Using an unpythonic loop
+========================
+
+Summary
+-------
+
+Instead of counting over an index and retrieving the corresponding index 
+element within the for loop, you should use enumerate to retrieve the 
+index and list element simultaneously.
+
+Description
+-----------
+
+`PEP 20 <http://legacy.python.org/dev/peps/pep-0020/>`_ states "There should be one-- and preferably only one --obvious way to do it." Creating a loop that uses an incrementing index to access each element of a list within the loop construct is not the preferred style for accessing each element in a list. The preferred style is to use ``enumerate()`` to simultaneously retrieve the index and list element simultaneously. 
+
+Examples
+----------
+
+Loop defines index and accesses each list element with index
+............................................................
+
+The module below uses an index variable ``i`` in a ``for`` loop to iterate through the elements of a list. This is not the preferred style for iterating through a list in Python.
+
+.. warning:: The code below is an example of an error. Using this code will create bugs in your programs!
+
+.. code:: python
+
+    l = [1,2,3]
+
+    for i in range(0,len(list)):  # creating index variable
+        le = l[i]  # using index to access list
+        print i,le
+
+Solutions
+---------
+
+Retrieve index and element when defining loop
+.............................................
+
+The updated module below demonstrates the Pythonic style for iterating through a list. When you define two variables in a ``for`` loop in conjunction with a call to ``enumerate()`` on a list, Python automatically assigns the first variable as an index variable, and the second variable as the corresponding list element value for that index location in the list.
+
+.. code:: python
+
+    for i, le in enumerate(l):
+        print i, le
+    
+References
+----------
+- `PEP 20 - The Zen of Python <http://legacy.python.org/dev/peps/pep-0020/>`_
