Functions and Modules
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Introduction to python user defined function

User defined function are kind of functions which are defined by user in python program to do some specific tasks with specific requirements.

To define a function in python we use
def
keyword which means define. 
syntax:
def function_name(parameters) # code

example:
def print_hello(): print("hello world!") print_hello() # output: # hello world!
Passing parameters to a function

Parameters are basically placeholder which are used in a lot function to get actual value for the specific data inside of a function.

They work as a variable when we call a function.

syntax:
def function_name(parameter): x = <parameter> print(x) function_name(parameter)

example:
def pr nt_name(name): x = name print("Hello, ", name) print_name("Preet") # output: # Hello, Preet
Standard Library: Builtin functions

python has very large collection of built in functions which are used by user to make things easy in the program to be executed.

these are kind of function which doesnât require any installation or importing external data.

we can use these functions directly in our code by calling them with identifier.

here are few of the builtin function in python,

len()
 len function is used to find length of passed object.
my_list = [1,3,545,6,7,3,6] print(len(my_list))

print()
 print function is used to print any output on our console.
print("Hello world") print(143)

input()
 input function is used to take input from user, store it in variable and use later in our python program.
age = input("Enter your age: ") print("User is ", age, " years old!")

type()
 type function is used to find type of any object.
my_str = "Hello world!!" my_int = 143 print(type(my_str)) print(type(my_int))

min()
 min function is used to find minimum value from passed parameters.
print(min(3,5,2,5,7,3,1))

max()
 max function is used to find maximum value from passed parameters.
print(max(3,5,2,6,8,234,456,33,3))

sum()
 sum function is used to sum up two passed parameters.
x = 10 y = 20 print(sum(10,20))

etc.
Modules and Packages
Random Module

Random module in python is used to generate any random sequence of numbers or any other data.

This module is preinstalled in python so it doesnât require any external installation.

we can start using it by importing in our file â
import random

this module can help to generate series of random numbers or data.

here are few function from the random module
random.random()
 Returns random number between 0 and 1
 0.34244
random.randint()
 returns random integer.
random.range()
 generate sequence of number or data from given range.
random.randrange()
 generates series with random range.
random.choice()
 chooses random data from the given object.

Example:
import random my_list = ["red", "blue", "green"] random_color = random.choice(my_list) print(random_color) # output: # red
Math Module
 Math module in python is used to perform mostly all math function inside of python program.
 It is very useful when we have to perform such complex mathematic equation in our program to get some specific data.
 It is preinstalled in python programming language which means it doesnât require any external installation to start using this module.
import math

Here are few function from the math module

math.sum()
 Returns sum of two numbers
math.sum(10,20)

math.pow()
 Return answer of A to the B
math.pow(a,b)

math.exp()
 Returns exponential of the number
math.exp(65)

math.asin()
 Returns Arc sin of a number.

math.acos()
 Returns Arc cos of a number.

math.atan()
 Returns Arc tan of a number.

math.sin()
 Returns sin of a number.

math.cos()
 Returns cos of a number.

math.tan()
 Returns tan of a number.

math.log()
 Returns log of given number.

math.sqrt()
 Returns Square root of given number.
math.sqrt(25)

math.fact()
 Returns factorial of given number.
math.fact(25)

Datetime Module
 Datetime module in python is very useful module to easily manage the dates and current time data in program.
 It is preinstalled module in python so it doesnât require any external installation.
import datetime
 Datetime module has vast collection of datetime functions and methods.
 Here are few function from the datetime module.
datetime.date()
 Returns the current date.
datetime.time()
 Returns the current time.
datetime.datetime()
 Returns the current date and time.
datetime.timedelta()
 Returns the difference in date or time at any given point.
datetimte.tzinfo()
 Returns time zone information.
datetime.timezone()
 Returns time zone information with recent version of UTC.
Matplotlib Module
 Matplotlib means Math plot library.
 This is used to plot visual graph in python program for some specific data set or any online data.
 This isnât preinstalled in python so it requires installation before usage.
pip install matplotlib

matplotlib allows us wide variety of plots which helps to understand trends and patterns. Here are few of them listed,

Matplotlib Line Plot
 This plotting is used to plot graph with line visual.
from matplotlib import pyplot as plt x = [2,4,6] y = [2,7,2] plt.plot(x,y) plt.show()

Matplotlib Bar Plot
 This plotting is used to plot graph with bar visual.
from matplotlib import pyplot as plt x = [4,3,7] y = [2,6,8] plt.bar(x,y) plt.show()

Matplotlib Histogram Plot
 This plotting is used to plot graph with histogram visual.
from matplotlib import pyplot as plt x = [3,5,2] y = [8,7,3] plt.hist(x,y) plt.show()

Matplotlib Scatter Plot
 This plotting is used to plot graph with scatter visual.
from matplotlib import pyplot as plt x = [3,5,2] y = [8,7,3] plt.scatter(x,y) plt.show()

Matplotlib Pie Plot
 This plotting is used to plot graph with pie visual.
from matplotlib import pyplot as plt label = ["Day 1", "Day 2", "Day 3"] sizes = [35,35,30] plt.pie(sizes, labels=label) plt.title("Pie chart example") plt.show()

Create and import custom user defined modules
 creating custom user defined modules is very simple task here is how we can achieve that.
 first create a file named
matho.py
 now inside that file we define our user defined functions.
def sum(x,y):
return x + y
def sub(x,y):
return x  y
def multi(x,y):
return x * y
def mod(x,y):
return x % y
def div(x,y):
return x / y
 now in our main file
main.py
we can import our user defined module
import matho.py
a = 10
b = 20
print(matho.sum(a,b))
print(matho.sub(a,b))
print(matho.multi(a,b))
print(matho.mod(a,b))
print(matho.div(a,b))
 This is the most basic yet effective method to create userdefined functions and actually import them in our main file and use them easily.