Assert statements are a convenient way to insert debugging assertions into a program:
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
AssertionError refer to the built-in
variables with those names. In the current implementation, the
__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.
__debug__ are illegal. The value for the
built-in variable is determined when the interpreter starts.
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