DEV Community: importox

Sys Module with Examples in Python

importox — Tue, 09 Jun 2020 12:49:06 +0000

The sys module has access to some variables used by the interpreter.

In this article you'll see some sys module examples in the Python programming language.

Python sys Module

The sys module provides you with details about the Python interpreter. Note that if you want to do things with the operating system like running a program you can use the os module instead.

This module is one of the best Python modules, and if you want to use the sys module, you need to import it into the program like other built-in modules.

This provides a lot of information about the Python interpreter, such as the version of the interpreter, the maximum value that the variable can hold, the copyright information of the Python interpreter, etc.

Here, with an example, you can see some important functions of the sys module.

You can try this from both the shell and from a script.

Important functions of the sys module are shown below.

1) sys.version

This function returns the version of the Python interpreter in string format with the date of the installation.

Python Example:

    # Importing the module
    import sys

    # Printing the python version
    print(sys.version)

The program above outputs this:

3.7.7 (default, Mar 13 2020, 10:23:39) \n[GCC 9.2.1 20190827 (Red Hat 9.2.1-1)]

2) sys.copyright

This function returns information about the copyright of the Python interpreter.

Python Example:

    # Importing the sys module
    import sys

    # Printing copyright info
    print('Information about copyright:')
    print(sys.copyright)

The program above outputs this:

'Copyright (c) 2001-2020 Python Software Foundation.\nAll Rights Reserved.\n\nCopyright (c) 2000 BeOpen.com.\nAll Rights Reserved.\n\nCopyright (c) 1995-2001 Corporation for National Research Initiatives.\nAll Rights Reserved.\n\nCopyright (c) 1991-1995 Stichting Mathematisch Centrum, Amsterdam.\nAll Rights Reserved.'

3) sys.maxsize

This function returns the maximum value of int that a variable can take.

Python Example:

    # Importing the sys module
    import sys

    # Printing the max value of an int
    print('Maximum value of an int:',sys.maxsize)

The program above outputs this:

Maximum value of an int: 9223372036854775807

sys.path

This function returns a list which includes all Python modules in the search path.

Python Example:

    # Importing the sys module
    import sys

    # Printing the all path
    print('List of the all paths:')
    print(sys.path)

The program above outputs this:

List of the all path: ['/home/frank', '/usr/lib64/python37.zip', '/usr/lib64/python3.7', '/usr/lib64/python3.7/lib-dynload', '/home/frank/.local/lib/python3.7/site-packages', '/home/frank/.local/lib/python3.7/site-packages/tpass-0.1.8-py3.7.egg', '/home/frank/.local/lib/python3.7/site-packages/simplejson-3.17.0-py3.7.egg', '/home/frank/.local/lib/python3.7/site-packages/pyperclip-1.8.0-py3.7.egg', '/usr/lib/python3.7/site-packages', '/usr/lib64/python3.7/site-packages']

Read more

with keyword with example

importox — Tue, 09 Jun 2020 11:59:45 +0000

The Python with keyword with is a keyword in python, it is similar to the "using" statement in VB.net or/and C#.net. Keywords are case-sensitive in Python.

It creates a with-block that executes that uses the variables which are declared in the with keyword.

with keyword is used to make sure that the exit method is called when the block ends. It's like a try-except block.

If you use files in Python, you may use the with keyword for opening a file, with block may contain the file operations. And after the block execution, the file will be closed, even if there are errors.

The with keyword can be used in the shell and from a python script.

Syntax of with keyword

The syntax of the with keyword is:

        with expression [as variable]:
            with-block-statement(s)

Python Example:

The example below uses the with keyword to write a file. This is easier than manually having to close the file.

        # opening a file and creating with-block
        with open(file_name, "w") as thefile:
            thefile.write("Hello devto!")

Python example of with keyword

Use the with keyword to open a file and write the text

    # example with keyword
    # Use "with" to open and write file

    # file name
    file_name = "file1.txt"

    # open a file using with-block
    with open(file_name, "w") as thefile:
        thefile.write("Hello devto!")

    # make sure file is closed
    if thefile.closed:    
        print("File is closed")

The program above outputs this:

File is closed

Cotent of the file:

Hello devto!

Related links:

Tuples in Python

importox — Tue, 09 Jun 2020 11:33:04 +0000

Python Tuples basic concepts are introduced in this aritcle.
Tuples in Python with some examples. A tuple is one of Python's data types

Python Tuples

Python tuples are a group of elements separated by commas in a round bracket.

Tuples are like list, they are a sequence. You can get the index, get a slice etc.

But lists are mutable whereas tuples are immutable.

A Python tuple can be cast into list in Python with the keyword list(). A Python list can be cast into tuples by using keyword "tuple".

Here you will see some examples to understand how to create tuples? ,convert lists into tuples? , concatenation of tuples , nestedtuples , etc.

This works in both the Python shell and from a Python script

Creating Tuples

    tup='Python','Tuple','Lists'
    tup2=('Python','Tuple','Lists','Devto','best')

    e_tup=()

    u_l_tup=('devto',)

    print('empty tuple:',e_tup)
    print('Unit length tuple:',u_l_tup)
    print('first tuple:',tup)
    print('Second tuple:',tup2)

Note: When you are going to create a tuple of length 1 in Python then you should put a comma after the element before closing the round brackets.

The program above outputs this:

    empty tuple: ()
    Unit length tuple: ('devto',)
    first tuple: ('Python', 'Tuple', 'Lists')
    Second tuple: ('Python', 'Tuple', 'Lists', 'Devto', 'best')

Here, you have seen that if you are creating tuples with round brackets or not both results are the same.

Concatenation of Tuples

Add tuples like lists by using plus (+) sign between it. Let's suppose the same tuples that you have created just above and try to add these tuples.

Program:

    tup1  = 'Python','Tuple','Lists'
    tup2 = ('Python','Tuple','Lists','Devto','best')

    print('Concatenation of Tuples:\n',tup1+tup2)

The program above outputs this:

    Concat of tuples: 
    ('Python', 'Tuple', 'Lists', 'Python', 'Tuple', 'Lists', 'Devto', 'best')

Convert list into tuples and tuples into list

    tup=('Python','Tuple','Lists','Devto','best')

    l=list(tup) #now l is list.
    tup2=tuple(l) #Here list is converted into tuple.

    print('tuple is converted into list:',tup)
    print('list is converted into tuple:',tup2)

The program above outputs this:

tuple is converted into list: ['Python', 'Tuple', 'Lists', 'Devto', 'best']
list is converted into tuple: ('Python','Tuple','Lists','Devto','best')

Nested tuples

Nested tuples means one tuple inside another (this is like nested lists).

To create a nested tuple , you have to put both or more tuples in the round brackets separated with commas.

Let's look at this Python program,

    tup='Python','Tuple','Lists'
    tup2=('Python','Tuple','Lists','Devto','best')

    nested_tup=(tup,tup2)

    print('Nested tuple:',nested_tup)

The program above outputs this:

Nested tuple: (('Python', 'Tuple', 'Lists'), ('Python', 'Tuple', 'Lists', 'Devto', 'best'))

Related links

How to write in an existing file in Python?

importox — Tue, 09 Jun 2020 11:10:03 +0000

You are going to learn how to write text in an existing file in python?

Python can work with files, it can read files, write file and even read csv files. In brief, any data can be read by Python.

You can use the open(filename,mode) function to open a file. There are a set of file opening modes.

To write in an existing file you have to open the file in append mode("a") , if the file does not exist, the file will be created.

To write text in an existing file , first step is to verify if the file exists or not?

If the file you want to write to does not exist, program will create a new file.

append to file

In this Python example, it creates a file, write a string and then closes the file. After that, you will open the file in append mode "a" .

    # write lines to an existing file
    # after creating it    
    fo = open("example1.txt", "w")
    fo.write("Hello world.")
    fo.close()

Now that you have a file, you can append to it

    # open the file in append mode
    fo = open("example1.txt","a")
    fo.write("I like Python")
    fo.close()

If you want you can read and display it

    # read and display the file 
    fo = open("example1.txt","r")
    print("The file contains: ")
    dummy = fo.read()
    print(dummy)   
    fo.close()

The program above outputs this:

The file contains: 
Hello world.I like Python

This works in both the Python shell and running from a file.

pprint (Pretty Printer) in Python

importox — Tue, 09 Jun 2020 10:49:10 +0000

In this Python tutorial, you are going to learn about a very useful inbuilt module in python that is called pprint().

pprint is a python module that helps you to _make the readability of a complex data structures easy.

The pprint is also called as "prettyprint".

You can see an example below with a dictionary.

    # define dictionary
    dictionary = {"id": 1,"name": "Leanne Graham","username": "Bret","email": "Sincere@april.biz","address": {  "street": "Kulas Light",  "suite": "Apt. 556",  "city": "Gwenborough",  "zipcode": "92998-3874",  "geo": {    "lat": "-37.3159",    "lng": "81.1496"  }},"phone": "1-770-736-8031 x56442","website": "hildegard.org","company": {  "name": "Romaguera-Crona",  "catchPhrase": "Multi-layered client-server neural-net",  "bs": "harness real-time e-markets"}}

    # output the dictionary
    print(dictionary)

The above program outputs:

    {'id': 1, 'name': 'Leanne Graham', 'username': 'Bret', 'email': 'Sincere@april.biz', 'address': {'street': 'Kulas Light', 'suite': 'Apt. 556', 'city': 'Gwenborough', 'zipcode': '92998-3874', 'geo': {'lat': '-37.3159', 'lng': '81.1496'}}, 'phone': '1-770-736-8031 x56442', 'website': 'hildegard.org', 'company': {'name': 'Romaguera-Crona', 'catchPhrase': 'Multi-layered client-server neural-net', 'bs': 'harness real-time e-markets'}}

As you can see, the output is not in a proper and readable way , you cannot read this complex nested dictionary structure.

To solve this issue of readability you can use the inbuilt module pprint.

Downloading pprint Module

You can use pip to install the module. In your terminal or command prompt, type the following command:

pip install pprint

Using pycharm: Go to the project interpreter and install the module.

pprint example

Now after installing, import the module and there is a _function in this module named pprint so import that as _

from pprint import pprint

To make the structure look good just pprint() instead of print().

    from pprint import pprint

    dictionary = {"id": 1,"name": "Leanne Graham","username": "Bret","email": "Sincere@april.biz","address": {  "street": "Kulas Light",  "suite": "Apt. 556",  "city": "Gwenborough",  "zipcode": "92998-3874",  "geo": {    "lat": "-37.3159",    "lng": "81.1496"  }},"phone": "1-770-736-8031 x56442","website": "hildegard.org","company": {  "name": "Romaguera-Crona",  "catchPhrase": "Multi-layered client-server neural-net",  "bs": "harness real-time e-markets"}}

    # output the dictionary
    pprint(dictionary)

The above program outputs the clear and easily readable:

{'address': {'city': 'Gwenborough',
             'geo': {'lat': '-37.3159', 'lng': '81.1496'},
             'street': 'Kulas Light',
             'suite': 'Apt. 556',
             'zipcode': '92998-3874'},
 'company': {'bs': 'harness real-time e-markets',
             'catchPhrase': 'Multi-layered client-server neural-net',
             'name': 'Romaguera-Crona'},
 'email': 'Sincere@april.biz',
 'id': 1,
 'name': 'Leanne Graham',
 'phone': '1-770-736-8031 x56442',
 'username': 'Bret',
 'website': 'hildegard.org'}

This also works in the Python shell