What does __name__ == "__main__" mean?

When you run a python script directly (example: $ python script.py), you want to set a starting point of the script. Python scripts are interpreted from the first line, then goes to the second line and so on ...

import module

def my_function():
  # code here

x = my_function()

But you want to make your code more structured, so you come up with this:

import module

def my_function():
  # code here

def main():
  x = my_function()

# the program starts from here
main()

This is good, but problem is, if you import the script from another script (from module import *), the main() function gets executed, but you may not want to do this. You want to call the main() function only when this script is exclusively executed. And you can do this using __name__ == "__main__".

import module

def my_function():
   # code here

def main():
   x = my_function()

# the program starts from here
if __name__ == "__main__":
   main()

Thus you can make your script to make it a reusable script (import from another script) and a standalone script as well.

Comments

Unknown said…
Thank you for clear discussion
January 12, 2015 at 10:05 AM
jaskaran said…
Can you explain little bit more, I can not understand this :(


This is good, but problem is, if you import the script from another script (from module import *), the main() function gets executed, but you may not want to do this. You want to call the main() function only when this script is exclusively executed. And you can do this using __name__ == "__main__".

February 5, 2015 at 10:44 AM
Tamim Shahriar said…
Say you have a script named math.py that has a function named add(x, y). Now in another python file if you need to use this add function, you need to import math. But in your math.py file, if there is some test code like print add(5, 5), it will also get executed. So you should write the test code in math.py file inside the if block (if __name__ == "__main__"). So only when you run math.py file exclusively, it will run, otherwise not.
February 5, 2015 at 11:31 AM
Post a Comment

Popular posts from this blog

Strip HTML tags using Python

We often need to strip HTML tags from string (or HTML source). I usually do it using a simple regular expression in Python. Here is my function to strip HTML tags: def remove_html_tags(data): p = re.compile(r'<.*?>') return p.sub('', data) Here is another function to remove more than one consecutive white spaces: def remove_extra_spaces(data): p = re.compile(r'\s+') return p.sub(' ', data) Note that re module needs to be imported in order to use regular expression. Here you can find an updated code that gets the text from html: http://love-python.blogspot.com/2011/04/html-to-text-in-python.html
Read more

lambda magic to find prime numbers

Find prime number up to 100 with just 3 lines of code. The 4th line is for printing ;) nums = range(2, 100) for i in range(2, 10):     nums = filter(lambda x: x == i or x % i, nums) print nums Isn't it amazing? Check my new post about Prime number: http://love-python.blogspot.com/2010/11/prime-number-generator-in-python-using.html
Read more

Convert text to ASCII and ASCII to text - Python code

Python has a very simple way to convert text to ASCII and ASCII to text. To find the ASCII value of a character use the ord() function. Example: >>> ord('B') 66 To get a character from it's ASCII value use the chr() function. Example: >>> chr(65) 'A' Here is a program to get the list of all characters along with their values: # program to print the list of characters and their ASCII values for value in range(0, 255): print "ASCII Value:", value, "\t", "Character:", chr(value), "\n" Here is another simple ASCII encoding-decoding program: # Convertion from text to ASCII codes message = raw_input("Enter message to encode: ") print "Decoded string (in ASCII):" for ch in message: print ord(ch), print "\n\n" # Convertion from ASCII codes to text message = raw_input("Enter ASCII codes: ") decodedMessage = "" for item in message.split(): decodedMessage += chr...
Read more