Call-by-object parameter passing in Python

call_by_object_example.py

# Passing a mutable object to a function is like passing a C-pointer to
# the memory location of the object -> mutating memory inside the function
# will be "visible" outside the function too.
# Since each function has its own _namespace_, mangling the variable
# is equivalent to moving the pointer away from the passed-in location
# so any changes to the parameter variable remain within the scope of
# the function.

outer_list = [1,2,3,4]

def double_last_element(inner_list):
  inner_list[-1] *= 2
  print('inner_list after doubling', inner_list)
  # Then mangle the variable in the function's namespace
  inner_list = ['a', 'b', 'c', 'd']
  print('inner_list after mangling', inner_list)
  
double_last_element(outer_list)
print('outer_list after function call', outer_list)