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Assert statements are a convenient way to insert debugging assertions into a program:
| assert_stmt | ::= | "assert" expression ["," expression] |
The simple form, "assert expression", is equivalent to
if __debug__: if not expression: raise AssertionError
The extended form, "assert expression1, expression2", is equivalent to
if __debug__: if not expression1: raise AssertionError, expression2
These equivalences assume that __debug__ and
AssertionError refer to the built-in
variables with those names. In the current implementation, the
built-in variable __debug__ is True under normal
circumstances, False when optimization is requested (command line
option -O). The current code generator emits no code for an assert
statement when optimization is requested at compile time. Note that it
is unnecessary to include the source code for the expression that failed
in the error message;
it will be displayed as part of the stack trace.
Assignments to __debug__ are illegal. The value for the
built-in variable is determined when the interpreter starts.
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