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Highlights from this chapter include:

  • Functions are named blocks of code that perform tasks when called and make programs more organized and optimized.
  • Control flow is the sequence of program execution. Control flow moves between calling code and function code when a function is called.
  • Variable scope refers to where a variable can be accessed. Global variables can be accessed anywhere in a program. Local variables are limited in scope, such as to a function.
  • Parameters are function inputs defined with the function. Arguments are values passed to the function as input by the calling code. Parameters are assigned with the arguments' values.
  • Function calls can use positional arguments to map values to parameters in order.
  • Function calls can use keyword arguments to map values using parameter names in any order.
  • Functions can define default parameter values to allow for optional arguments in function calls.
  • Python uses a pass-by-object-reference system to assign parameters with the object values referenced by the arguments.
  • Functions can use return statements to return values back to the calling code.

At this point, you should be able to write functions that have any number of parameters and return a value, and programs that call functions using keyword arguments and optional arguments.

Construct Description
Function definition
def function_name():
  """Docstring"""
  # Function body
Parameter
def function_name(parameter_1):
  # Function body
Argument
def function_name(parameter_1):
  # Function body
    
function_name(argument_1)
Return statement
def function_name():
  # Function body
  return result # Returns the value of result to the caller
Variables (scope)
def function_name(parameter_1):
  # Function body
  local_var = parameter_1 * 5
  return local_var

global_var = function_name(arg_1)
Keyword arguments
def function_name(parameter_1, parameter_2):
  # Function body
    
function_name(parameter_2 = 5, parameter_1 = 2)
Default parameter value
def function_name(parameter_1 = 100):
  # Function body
Table 6.2 Chapter 6 reference.
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