GNU Info

(python2.1-ref.info)Assert statements

---

Next: Assignment statements Prev: Expression statements Up: Simple statements

---

Enter node , (file) or (file)node

Assert statements
=================

Assert statements  are a convenient way to insert debugging assertions
into a program:

     assert_statement: "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 1 under normal
circumstances, 0 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.