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Functions Style Notes

The suite within a compound statement is typically indented four spaces. It is often best to set your text editor with tab stops every four spaces. This will usually yield the right kind of layout.

We'll show the spaces explicitly as ␣'s in the following fragment.

def␣max(a,␣b):
␣␣␣␣if␣a␣>=␣b:
␣␣␣␣␣␣␣␣m␣=␣a
␣␣␣␣if␣b␣>=␣a:
␣␣␣␣␣␣␣␣m␣=␣b
␣␣␣␣return m

This is has typical spacing for a piece of Python programming.

Also, limit your lines to 80 positions or less. You may need to break long statements with a \ at the end of a line. Also, parenthesized expressions can be continued onto the next line without a \. Some programmers will put in extra ()'s just to make line breaks neat.

Names. Function names are typically mixedCase. However, a few important functions were done in CapWords style with a leading upper case letter. This can cause confusion with class names, and the recommended style is a leading lowercase letter for function names.

In some languages, many related functions will all be given a common prefix. Functions may be called inet_addr, inet_network, inet_makeaddr, inet_lnaof, inet_netof, inet_ntoa, etc. Because Python has classes (covered in Part III, “Data + Processing = Objects”) and modules (covered in Part IV, “Components, Modules and Packages”), this kind of function-name prefix is not used in Python programs. The class or module name is the prefix. Look at the example of math and random for guidance on this.

Parameter names are also typically mixedCase . In the event that a parameter or variable name conflicts with a Python keyword, the name is extended with an _. In the following example, we want our parameter to be named range , but this conflicts with the builtin function range. We use a trailing _ to sort this out.

def integrate( aFunction, range_ ):
    """Integrate a function over a range."""
    
...

Blank lines are used sparingly in a Python file, generally to separate unrelated material. Typicaly, function definitions are separated by single blank lines. A long or complex function might have blank lines within the body. When this is the case, it might be worth considering breaking the function into separate pieces.

Docstrings. The first line of the body of a function is called a docstring. The recommended forms for docstrings are described in Python Extension Proposal (PEP) 257.

Typically, the first line of the docstring is a pithy summary of the function. This may be followed by a blank line and more detailed information. The one-line summary should be a complete sentence.

def fact( n ):
    """fact( number ) -> number
    
    Returns the number of permutations of n things."""
    if n == 0: return 1L
    return n*fact(n-1L)

def bico( n, r ):
    """bico( number, number ) -> number
    
    Returns the number of combinations of n things 
    taken in subsets of size r.
    Arguments:
    n -- size of domain
    r -- size of subset
    """
    return fact(n)/(fact(r)*fact(n-r))

The docsting can be retrieved with the help function.

help ( object )

Type help for interactive help, or help ( object ) for help about object .

Here's an example, based on our fact shown above.

>>> 

help(fact)


Help on function fact in module __main__:

fact(n)
    fact( number ) -> number

    Returns the number of permutations of n things.


 
 
  Published under the terms of the Open Publication License Design by Interspire