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(python2.1-ref.info)Introduction

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Introduction
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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 a second one now exists!), 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
document.  A few built-in modules are mentioned when they interact in a
significant way with the language definition.

Notation