We're back after a server migration that caused effbot.org to fall over a bit harder than expected. Expect some glitches.

Syntax: Statements

Simple Statements

Simple statements are comprised within a single logical line. Several simple statements may occur on a single line separated by semicolons. The syntax for simple statements is:

Compound Statements

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 and with specifies exception handlers and/or cleanup code for a group of statements. Function and class definitions (def and class) 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. The suite is usually written as one or more indented statements on subsequent lines.

keyword expression :
    statement
    statement

A suite can also be one or more semicolon-separated simple statements on the same line as the header, following the header’s colon.

keyword expression : statement ; statement

The latter form cannot 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][1] | [while\_stmt][2] | [ for\_stmt][3] | [ try\_stmt][4] | [ with\_stmt][5] | [funcdef][6] | [ classdef][7] suite ::= [ stmt_list][8] NEWLINE | NEWLINE INDENT [statement][9]+ DEDENT statement ::= [ stmt_list][8] NEWLINE | [compound_stmt][10] stmt_list ::= [ simple_stmt][11] (“;” [simple_stmt][11])* [“;”]

Note that statements always end in a NEWLINE possibly followed by a DEDENT token. 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).