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(python2.1-ref.info)Compound statements

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Compound statements
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Compound statements contain (groups of) other statements; they affect
or control the execution of those other statements in some way.  In
general, compound statements span multiple lines, although in simple
incarnations a whole compound statement may be contained in one line.

The `if', `while' and `for' statements implement traditional control
flow constructs.  `try' specifies exception handlers and/or cleanup
code for a group of statements.  Function and class definitions are
also syntactically compound statements.

Compound statements consist of one or more `clauses.'  A clause
consists of a header and a `suite.'  The clause headers of a particular
compound statement are all at the same indentation level.  Each clause
header begins with a uniquely identifying keyword and ends with a
colon.  A suite is a group of statements controlled by a clause.  A
suite can be one or more semicolon-separated simple statements on the
same line as the header, following the header's colon, or it can be one
or more indented statements on subsequent lines.  Only the latter form
of suite can contain nested compound statements; the following is
illegal, mostly because it wouldn't be clear to which `if' clause a
following `else' clause would belong:

     if test1: if test2: print x

Also note that the semicolon binds tighter than the colon in this
context, so that in the following example, either all or none of the
`print' statements are executed:

     if x < y < z: print x; print y; print z

Summarizing:

     compound_stmt:  if_stmt | while_stmt | for_stmt
                   | try_stmt | funcdef | classdef
     suite:          stmt_list NEWLINE | NEWLINE INDENT statement+ DEDENT
     statement:      stmt_list NEWLINE | compound_stmt
     stmt_list:      simple_stmt (";" simple_stmt)* [";"]

Note that statements always end in a `NEWLINE'  possibly followed by a
`DEDENT'.   Also note that optional continuation clauses always begin
with a keyword that cannot start a statement, thus there are no
ambiguities (the `dangling `else'' problem is solved in Python by
requiring nested `if' statements to be indented).

The formatting of the grammar rules in the following sections places
each clause on a separate line for clarity.

if statement

while statement

for statement

try statement

Function definitions

Class definitions