Python Programming - Functions and Modules

CS.QIAU - Winter 2020
PYTHONFunctions and Modules - Session 3
Omid AmirGhiasvand
Programming

also called Procedural
PROGRAMMING
IS A TYPE OF IMPERATIVE
PROGRAMMING PARADIGM
STRUCTURED

PROGRAMMING IS A
PROGRAMMING PARADIGM THAT USES
STATEMENTS THAT CHANGE A
PROGRAM’S STATE.
IMPERATIVE

PROGRAMMING IS
APROGRAMMING PARADIGM THAT
EXPRESSES THE LOGIC OF A
COMPUTATION WITHOUT DESCRIBING ITS
CONTROL FLOW.
DECLARATIVE

IMPERATIVE VS.
DECLARATIVEHuge paradigm shift. Are you ready?

Function
▸ Function is a named block of code that is design to do a specific job.
▸ The basic idea is write the code once and use it again and again. The first
step to code reuse.
▸ You can call the function whenever you like in your code.
1. def function_name(paramter_1,parameter_2,…):
2. someCode
3. someCode
4. someCode
5. return someValue
“function name” is an identifier so it must follow identifier naming rules!
Positional
Parameters - The
order matters

FUNCTIONS MUST BE
BEFORE BEING CALLED.
DEFINED

Example of Defining and Calling a Function
▸ Function without parameters
▸ Function with parameters
▸ Calling a function with or without arguments
1. def welcome_passenger():
2. print(“Dear Passenger welcome onboard ”)
1. def welcome_passenger(passengerName):
2. print(“Dear Mr/Ms” + passengerName + “ Welcome Onboard”)
1. welcome_passenger()
2. welcome_passenger(“Tehrani”)
parameter
argument

we can use
pass as a place
holder

P A R A M E T E R V S .
ARGUMENT
Two names for the same things. Parameters are inside
the function and Arguments are outside the function

Parameters Default Values
▸ We can deﬁne a default value for each parameter. If an argument for
for a parameters is provided in the function call python use the
argument value and if not its uses the parameter’s default value
1. def welcome_message(name, country =“Japan”):
2. print(“Mr./Ms. ” + name + “ from ”+country + “ Welcome To Iran” )
1. welcome_message(name=“John”, country=”Germany”)
2. welcome_message(name=“John”,)
Be careful about Arguments Error
“Japan” is the
default value

Return a Value
▸ Function can process some data and then return a value or set of
values
▸ Calling the function with return value
1. def format_name(ﬁrst_name, last_name):
2. full_name = ﬁrst_name.title() + “ “ + last_name.title()
3. return full_name
1. print(format_name(“ehsan”,”kaviani”))
2. formated_name = formated_name(“ehsan”,”Kaviani”)

Return Multiple Value
▸ A Function can return any object including data structures like
dictionary or list.
1. def add_key_value(dic,key,value):
2. dic[key] = value
3. return dic
5. student_dic_0 = {“name” : ”Kaveh” , “family”:”Sarkhosh”}
6. student_dic_0 = add_key_value(student_dic_0, ‘age’, 20)
7. print(student_dic_0)
It is a Dictionary
data structure

WHEN YOU PASS A LIST OR
DICTIONARY ANY CHANGE TO
THE OBJECT IS PERMANENT!
So be careful when you are working with list or dictionary

Keyword Arguments
▸ Is a name-value pair that you pass to a function
▸ Calling the function
1. def welcome_message(name, country ):
2. print(“Mr./Ms. ” + name + “ from ”+country + “ Welcome To Iran” )
1. welcome_message(name=“John”, country=”Germany”)
2. welcome_message(country=”Iran”, name=“Babak”)
You have to use the exact names of the parameters!!!! Exact

Pass Variable Number of Arguments
▸ *args and **kwargs are used as parameters in function deﬁnitions and
allows to pass a variable number of arguments to the calling function.
▸ *args allows you to pass a non-keyworded, variable length tuple
argument list to the
▸ **kwargs allows you to pass keyworded, variable length dictionary
argument list to the calling function

Example of Function With Variable Number of Parameters
▸ It should be noted that the single asterisk (*) and double asterisk (**) are
the important elements here and the words args and kwargs are used
only by convention.
1. def sample_function(name,*args,**kwargs):
2. print(f”Hello {name} here is the list of item you sent:”)
3. for item in args :
4. print(item)
5. print(f”Also here is the list of key-value you have sent:”)
6. for kw in kwargs :
7. print(kw,” : ”,kwargs[kw])

BY USING FUNCTION
YOU CAN SEPARATE
BLOCK OF CODE FROM
YOUR MAIN CODE
The code is much more readable and manageable

Using Modules
▸ You can store your functions in separate ﬁle called module and then
import the module in your main program.
▸ Module is a ﬁle with .py extension.
▸ You can put all functions in a module.
1. def add_key_value(dic,key,value):
2. dic[key] = value
3. return dic
my_module.py

Importing an Entire Module - All its Functions
▸ You can use a module by importing it wherever you need the module
function!
▸ Put the import at the top of your main code.
▸ The general rule is you have to deﬁne a function before you use it.
1. import my_module
2. #or
3. from my_module import *
main.py
There is a small difference between these two!!! What is it?

my_functions.py
in the root of the
project
we can add
function here

Python Programming - Functions and Modules

import
my_function
module
we have
to write imported
module name

did you get
what just
happened?

Importing Specific Function
▸ There is some big module with lots of function. But we just want to use
some speciﬁc functions so we can partially import the module.
1. from my_module import function_1, function_2
2. …
main.py

Aliasing Module Name or Function Name
▸ We can use alias to make module name shorter
1. import tensorﬂow as tf
2. from tensorﬂow.core import debug as tfd
main.py

THERE ARE MANY
MODULES THAT YOU CAN
USE IN YOUR PROGRAM
Using pip directly or using pip in pyCharm

Python Standard Libraries and Modules
▸ Built-in modules are part of python standard library
▸ python library reference manual
1. import math
2. import pathlib
3. import os
4. import json
5. import csv
6. …
https://docs.python.org/3/library/

very clean main
function
list of ﬁles and directory
in data directory

importing Path
p reference current
directory

list of ﬁles and directory
in project root

Python Third-Party Libraries and Modules - Package
▸ Third-party modules or libraries can be installed and managed using
Python’s package manager pip.
▸ You can use Operating System Command line
▸ You can use PyCharm Command Line
▸ You can use PyCharm Package Management Tool
pip install module_name

Preference
menu
Package
installed in project
venv
Python Interpreter
setting
To Install new
Package

numpy and
pandas are installed

IN PYTHON FUNCTION
IS AN OBJECTcan be assigned to a variable

try to understand
what just happened

“The Unexamined Life Is Not Worth Living”

Python Programming - Functions and Modules

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