Modules in Python

 

What is a Module?

Consider a module to be the same as a code library.

A file containing a set of functions you want to include in your application.

Create a Module:-

To create a module just save the code you want in a file with the file extension .py:

Example

Save this code in a file named mymodule.py

def greeting(name):
  print("Hello, " + name)

Use a Module:-

Now we can use the module we just created, by using the import statement:

Example

Import the module named mymodule, and call the greeting function:

import mymodule

mymodule.greeting("Jonathan")

Note: When using a function from a module, use the syntax: module_name.function_name.

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Variables in Module

The module can contain functions, as already described, but also variables of all types (arrays, dictionaries, objects etc):

Example

Save this code in the file mymodule.py

person1 = {
  "name": "John",
  "age": 36,
  "country": "Norway"
}

Example

Import the module named mymodule, and access the person1 dictionary:

import mymodule

a = mymodule.person1["age"]
print(a)

Python Datetime:-

A date in Python is not a data type of its own, but we can import a module named datetime to work with dates as date objects.

Example

Import the datetime module and display the current date:

import datetime

x = datetime.datetime.now()
print(x)

Date Output:-

When we execute the code from the example above the result will be:

2020-08-13 12:30:24.912671

The date contains year, month, day, hour, minute, second, and microsecond.

The datetime module has many methods to return information about the date object.

Here are a few examples, you will learn more about them later in this chapter:

Example

Return the year and name of weekday:

import datetime

x = datetime.datetime.now()
print(x.year)
print(x.strftime("%A"))

Creating Date Objects

To create a date, we can use the datetime() class (constructor) of the datetime module.

The datetime() class requires three parameters to create a date: year, month, day.

Example

Create a date object:

import datetime
x = datetime.datetime(2020, 5, 17)
print(x)

The datetime() class also takes parameters for time and timezone (hour, minute, second, microsecond, tzone), but they are optional, and has a default value of 0, (None for timezone).

The strftime() Method

The datetime object has a method for formatting date objects into readable strings.

The method is called strftime(), and takes one parameter, format, to specify the format of the returned string:

Example

Display the name of the month:

import datetime
x = datetime.datetime(2018, 6, 1)
print(x.strftime("%B"))

A reference of all the legal format codes:

Directive	Description	Example
%a	Weekday, short version	Wed
%A	Weekday, full version	Wednesday
%w	Weekday as a number 0-6, 0 is Sunday	3
%d	Day of month 01-31	31
%b	Month name, short version	Dec
%B	Month name, full version	December
%m	Month as a number 01-12	12
%y	Year, short version, without century	18
%Y	Year, full version	2018
%H	Hour 00-23	17
%I	Hour 00-12	05
%p	AM/PM	PM
%M	Minute 00-59	41
%S	Second 00-59	08
%f	Microsecond 000000-999999	548513
%z	UTC offset	+0100
%Z	Timezone	CST
%j	Day number of year 001-366	365
%U	Week number of year, Sunday as the first day of week, 00-53	52
%W	Week number of year, Monday as the first day of week, 00-53	52
%c	Local version of date and time	Mon Dec 31 17:41:00 2018
%x	Local version of date	12/31/18
%X	Local version of time	17:41:00
%%	A % character	%

Python Math:-

Python has a set of built-in math functions, including an extensive math module, that allows you to perform mathematical tasks on numbers.

Built-in Math Functions:-

The min() and max() functions can be used to find the lowest or highest value in an iterable:

Example

x = min(5, 10, 25)
y = max(5, 10, 25)

print(x)
print(y)

The abs() function returns the absolute (positive) value of the specified number:

Example

x = abs(-7.25)
print(x)

The pow(x, y) function returns the value of x to the power of y (xy).

Example

Return the value of 4 to the power of 3 (same as 4 * 4 * 4):

x = pow(4, 3)
print(x)

The Math Module

Python has also a built-in module called math, which extends the list of mathematical functions.

To use it, you must import the math module:

import math

When you have imported the math module, you can start using methods and constants of the module.

The math.sqrt() method for example, returns the square root of a number:

Example

import math

x = math.sqrt(64)
print(x)

The math.ceil() method rounds a number upwards to its nearest integer, and the math.floor() method rounds a number downwards to its nearest integer, and returns the result:

Example

import math

x = math.ceil(1.4)
y = math.floor(1.4)
print(x) # returns 2
print(y) # returns 1

The math.pi constant, returns the value of PI (3.14...):

Example

import math

x = math.pi
print(x)

Python JSON:-

JSON is a syntax for storing and exchanging data.

JSON is text, written with JavaScript object notation.

JSON in Python

Python has a built-in package called json, which can be used to work with JSON data.

Example

Import the json module:

import json

Parse JSON - Convert from JSON to Python

If you have a JSON string, you can parse it by using the json.loads() method.

The result will be a Python dictionary.

Example

Convert from JSON to Python:

import json

# some JSON:
x =  '{ "name":"John", "age":30, "city":"New York"}'
# parse x:
y = json.loads(x)
# the result is a Python dictionary:
print(y["age"])

Convert from Python to JSON

If you have a Python object, you can convert it into a JSON string by using the json.dumps() method.

Example

Convert from Python to JSON:

import json

# a Python object (dict):
x = {
  "name": "John",
  "age": 30,
  "city": "New York"
}
# convert into JSON:
y = json.dumps(x)
# the result is a JSON string:
print(y)