30_scope.md

def a_function(optional=None): ... print optional

a_function('foo') foo a_function() None

def another_function(optional=None): ... if optional is not None: ... print optional

another_function('foo') foo another_function()

def yet_another_function(optional=None): ... if optional is None: ... optional = 'default' ... print optional

yet_another_function('foo') foo yet_another_function() default

x = 4 def function_using_variable_from_global_scope(): ... print x

function_using_variable_from_global_scope() 4

def function_overwriting_variable_from_global_scope(): ... if y is None: ... y = 'default'

function_overwriting_variable_from_global_scope() Traceback (most recent call last): ... UnboundLocalError: local variable 'y' referenced before assignment

y = None function_overwriting_variable_from_global_scope() Traceback (most recent call last): ... UnboundLocalError: local variable 'y' referenced before assignment

y = 'asdf' function_overwriting_variable_from_global_scope() Traceback (most recent call last): ... UnboundLocalError: local variable 'y' referenced before assignment