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<qhelp>

<overview>

<p>The <code>for</code> statement is designed to allow you to iterate over the elements of a

sequence or other iterable object. Strings in Python are iterable, and often used as such.

However, they are also often considered, not as sequences of characters, but as atomic entities.

</p>

<p>

One source of defects in Python is mistakenly iterating over a non-iterable object such as an integer.

This sort of defect is easily detected as a <code>TypeError</code> will be raised. However, if a string

is mistakenly used as the iterable in a <code>for</code> statement, which also receives other sequences

(such as lists) then the code will iterate over the string one character at a time.

This is probably not what the programmer intended and results in errors that are hard to find.

</p>

</overview>

<recommendation>

<p>Since this defect usually indicates a logical error, it is not possible to give a general method

for addressing the defect. However, adding a guard that checks that the iterator is not a string

could be worthwhile.

</p>

</recommendation>

<example>

<p>

In this example, the loop may iterate over <code>"Hello"</code> producing one character per line,

as well as over <code>[ "Hello", "World" ]</code>

It is likely that the programmer forgot to wrap the <code>"Hello"</code> in brackets.

</p>

<sample src="IterableStringOrSequence.py" />

</example>

<references>

<li>Python Language Reference: <a href="http://docs.python.org/reference/compound_stmts.html#the-for-statement">The for statement</a>,

<a href="http://docs.python.org/2.7/reference/datamodel.html#object.__iter__">object.__iter__</a>.</li>

<li>Python Standard Library: <a href="http://docs.python.org/dev/library/stdtypes.html#iterator-types">Iterator types</a>.</li>

<li>Scipy lecture notes: <a href="http://scipy-lectures.github.io/advanced/advanced_python/#iterators">Iterators,

generator expressions and generators</a>.</li>

</references>

</qhelp>