This reference manual describes the Python programming language.
It is not intended as a tutorial.
While I am trying to be as precise as possible, I chose to use English
rather than formal specifications for everything except syntax and
lexical analysis. This should make the document more understandable
to the average reader, but will leave room for ambiguities.
Consequently, if you were coming from Mars and tried to re-implement
Python from this document alone, you might have to guess things and in
fact you would probably end up implementing quite a different language.
On the other hand, if you are using
Python and wonder what the precise rules about a particular area of
the language are, you should definitely be able to find them here.
If you would like to see a more formal definition of the language,
maybe you could volunteer your time -- or invent a cloning machine
:-).
It is dangerous to add too many implementation details to a language
reference document -- the implementation may change, and other
implementations of the same language may work differently. On the
other hand, there is currently only one Python implementation in
widespread use (although alternate implementations exist), and
its particular quirks are sometimes worth being mentioned, especially
where the implementation imposes additional limitations. Therefore,
you'll find short ``implementation notes'' sprinkled throughout the
text.
Every Python implementation comes with a number of built-in and
standard modules. These are not documented here, but in the separate
Python Library Reference document. A few
built-in modules are mentioned when they interact in a significant way
with the language definition.
