Remove Dead Branches

This transform removes if statement branches that can never run because the condition is a constant.

An if statement with a constant False condition is removed, keeping its else branch. An if statement with a constant True condition is replaced by its body, dropping any else branch. Only the literals True and False are treated as constants; the condition is not otherwise evaluated, so a name such as DEBUG is left alone even if it was assigned a constant value.

A branch is only removed when doing so does not change the meaning of the program. A branch is kept if removing it would change the enclosing scope, for example if it contains a yield, a global or nonlocal declaration, or the only assignment to a local variable. At module and class scope, where name resolution is dynamic, unreachable assignments and imports are removed.

If a branch is removed and a statement is still required, it is replaced by a zero expression statement.

This transform also removes the if __debug__ branches marked by the Remove Debug transform, so enabling that transform requires this one to remain enabled.

This transform is safe and enabled by default. Disable it by passing the remove_dead_branches=False argument to the python_minifier.minify() function, or passing --no-remove-dead-branches to the pyminify command.

Example

Input

if False:
    print('never runs')

if True:
    print('always runs')
else:
    print('never runs')

DEBUG = False
if DEBUG:
    print('DEBUG is not a literal, so this is left alone')

Output

print('always runs')
DEBUG=False
if DEBUG:print('DEBUG is not a literal, so this is left alone')