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.