Chapter 2: Notes on “Dive Into Python” by Mark Pilgrim

April 22nd, 2009 | No Comments »

Declaring functions

def functionName(params):

Defining a function’s doc string

def functionName(params):
   """This is the explanation of the function, surrounded by triple quotes.
   Returns a string."""

Further reading on document strings:

• Python Enhancement Proposals (PEP) 257: Docstring Conventions
• PEP 8: Style Guide for Python Code
• Documentation Strings in Python Tutorial (2.5.2)

Import search path

When importing a module, python looks in several places as defined in sys.path:

>>> import sys
>>> sys.path
['C:\Python25\Lib\idlelib', 'C:\Python25\lib\site-packages\setuptools-0.6c7-py2.5.egg',
'C:\WINDOWS\system32\python25.zip', 'C:\Python25\DLLs', 'C:\Python25\lib',
'C:\Python25\lib\plat-win', 'C:\Python25\lib\lib-tk', 'C:\Python25',
'C:\Python25\lib\site-packages']
>>> sys
<module 'sys' (built-in)>
>>> sys.path.append('/my/new/path')

The last line illustrates how to add a path to look in.

Everything is an object

Everything is an object! Functions, modules, strings, lists, everything!  Python objects are objects in the sense that they can be passed as an argument to a function or be assigned to variables.

As an example, all functions have a built-in attribute called __doc__, which you can access like this:

>>> print importedModule.functionName.__doc__
This is the explanation of the function, surrounded by triple quotes.
Returns a string.

Further reading on objects:

• “Objects, values, and types” in the Python Reference Manual
• “Python Objects” on effbot.org

Indenting code

As a newbie to Python, the built-in syntax rules are particularly appealing to me.

There are no braces for functions, no semicolons to end a line; simply indent and a code block is defined (for if statements, functions, etc.).  The only delimiter here is the colon”:”.

Further reading on indenting code:

• “Indentation” in the Python Reference Manual
• PEP 8: Style Guide for Python Code

Testing modules with if __name__

All modules have a built-in attribute __name__.  The value of this attribute depends on how the module is being used; is it imported or run on its own?

• If the module is imported, __name__ equals the filename (without path, without file extension)
• If the module is run as a stand-alone program, the value of __name__ is a special default value, __main__

Why is this important? It means that you can embed a test suite in the module itself.  In other words, it’s code that will only execute when running the module directly, not when it’s being imported.  To do this, you would include the following in the module:

if __name__ == "__main__":
    """Insert test code here."""

Further reading on importing modules:

• “The import statement” in the Python Reference Manual

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