Python 2.7 quick reference

Positional arguments do not begin with a hyphen. When there are multiple positional arguments, the meaning of each one is inferred from their position relative to the other positional arguments.

Optional arguments begin with a hyphen. In general each optional argument may have two forms, a short form consisting of a hyphen and a letter (e.g., “-h” for help), and a long form consisting of two hyphens and a full name (e.g., “--help”). Generally optional arguments are not required, but your program can make them required if you wish.

Some optional arguments may allow or require a value. For example, let's suppose your script has an option that specifies the name of a river, and that the short form is “-r” and the long form is “--river”. On the command line, the user can specify the Nile in any of these four ways:

-r Nile
-rNile
--river Nile
--river=Nile

Users may group multiple short-form options together. For example, if a script named sss has options “-a”, “-m”, “-p”, and “-s”, these two examples are valid and equivalent:

sss -a -m -p -s
sss -spma

A short-form option that takes an argument may occur as part of such a group, but only if it is the last option in the group.

Contrary to Unix practice, optional arguments may occur anywhere relative to the positional arguments. Also, the names of long-form optional arguments may be abbreviated if the abbreviation is unambiguous. For example, if a script has two long-form options --pratt and --polonius, option --pr will be accepted as an abbreviation for --pratt; but --p would not be acceptable because it is ambiguous.