system, like Java, have an advantage ... they can catch such errors at compile time (but of course you
have to maintain all that type information ... it's a tradeoff).
Variable Names
Since Python variables don't have any type spelled out in the source code, it's extra helpful to give
meaningful names to your variables to remind yourself of what's going on. So use "name" if it's a single
name, and "names" if it's a list of names, and "tuples" if it's a list of tuples. Many basic Python errors
result from forgetting what type of value is in each variable, so use your variable names (all you have
really) to help keep things straight.
Modules and Imports
One file of Python code is called a *module*. The file "binky.py" is also known as the module "binky". A
module essentially contains variable definitions like, "x = 6" and "def foo()". Suppose the file "binky.py"
contains a "def foo()". The fully qualified name of that foo function is "binky.foo". In this way, various
Python modules can name their functions and variables whatever they want, and the variable names
won't conflict -- module1.foo is different from module2.foo.
For example, we have the standard "sys" module that contains some standard system facilities, like the
argv list, and exit() function. With the statement "import sys" you can can then access the definitions in
the sys module and makes them available by their fully-qualified name, e.g. sys.exit().
import sys
# Now can refer to sys.xxx facilities
sys.exit(0)
There is another import form that looks like this: "from sys import argv, exit". That makes argv and exit()
available by their short names; however, we recommend the original form with the fully-qualified names
because it's a lot easier to determine where a function or attribute came from.
There are many modules and packages which are bundled with a standard installation of the Python
interpreter, so you don't have do anything extra to use them. These are collectively known as the "Python
Standard Library." Commonly used modules/packages include:
• sys -- access to exit(), argv, stdin, stdout, ...
• re -- regular expressions
• os -- operating system interface, file system
You can find the documentation of all the Standard Library modules and packages
at http://docs.python.org/library.
Online help and dir
There are a variety ways to get help for Python.
• Do a Google search, starting with the word "python", like "python list" or "python string lowercase". The
first hit is often the answer. This technique seems to work better for Python than it does for other
languages for some reason.
• The official Python docs site -- docs.python.org -- has high quality docs. Nonetheless, I often find a Google
search of a couple words to be quicker.
• There is also an official Tutor mailing list specifically designed for those who are new to Python and/or
programming!
• Many questions (and answers) can be found on StackOverflow.
• Use the help() [and dir()] functions described below.
Inside the Python interpreter, the help() function pulls up documentation strings for various modules,
functions, and methods. These doc strings are similar to Java's javadoc. This is one way to get quick
access to docs. Here are some ways to call help() from inside the interpreter:
• help(len) -- docs for the built in len function (note here you type "len" not "len()" which would be a call to
the function)
• help(sys) -- overview docs for the sys module (must do an "import sys" first)
• dir(sys) -- dir() is like help() but just gives a quick list of the defined symbols
• help(sys.exit) -- docs for the exit() function inside of sys
• help('xyz'.split) -- it turns out that the module "str" contains the built-in string code, but if you did not
know that, you can call help() just using anexample of the sort of call you mean: here 'xyz'.foo meaning
the foo() method that runs on strings
• help(list) -- docs for the built in "list" module
• help(list.append) -- docs for the append() function in the list module
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