Python Essential Reference, Second Edition

Documentation Strings

If the first statement of a module, class, or function definition is a string, that string becomes a documentation string for the associated object, as in the following example:

def fact(n): 
    "This function computes a factorial" 
    if (n <= 1): return 1 
    else: return n*fact(n-1) 

Code-browsing and documentation-generation tools sometimes use documentation strings. The strings are accessible in the _ _doc_ _ attribute of an object, as shown here:

>>> print fact._ _doc_ _ 
This function computes a factorial 
>>> 

The indentation of the documentation string must be consistent with all the other statements in a definition. Furthermore, adjacent strings appearing on different lines are not concatenated to form a single documentation ...