Python Snippets

Posted 2022-02-20 · Updated 2025-11-03

A collection of code snippets, small pearls of wisdom and bits of knowledge, that may come handy at times.

Don’t expect well thought out descriptions or highly structured content here; these are snippets.
(But there are some links spread around for further reading.)

You can also find some more practical functions in the Python area of my “misc_public” Git repository on BitBucket.org.

Contents

Don’t call your own module “test.py”

A file “test.py” that acts as a stand-alone script is fine, but a file with that name that should act as a module (i.e. to be imported by others) is problematic.

Example:

Module: X:\MyModules\test.py

def foo (i):
    print(i)

Script: X:\MyScripts\script1.py

sys.path.append('X:\\MyModules' )
import test

test.foo('bar')

That will produce this error message:

AttributeError: module 'test' has no attribute 'foo'

A check with help(test) will show you that Python’s own Regression tests package for Python will be used, not yours…

Check whether a certain version on Python is used

… exit if not:

import sys

if sys.version_info.major < 3 and sys.version_info.minor < 3:
	sys.exit("Python 3.3 or higher is required; you're running version " + 
              str(sys.version_info.major) + "." + str(sys.version_info.minor))

Command Line Arguments

With the sys module

The sys module provides system-specific parameters and functions

import sys

print("{0} CLI parameters: {1} ".format(str(len(sys.argv)), sys.argv))

print("1st parameter: {0}".format(sys.argv[0])) # Always the path to actual script.
if (len(sys.argv) >= 2): print("2nd parameter: {0}".format(sys.argv[1]))
if (len(sys.argv) >= 3): print("3rd parameter: {0}".format(sys.argv[2]))

Result:

> .\test.py foo "bar baz"
3 CLI parameters: ['C:\\devel\\_test\\test.py', 'foo', 'bar baz']
1st parameter: C:\devel\_test\test.py
2nd parameter: foo
3rd parameter: bar baz

With the argparse module

The argparse module comes with Python 2.7 and 3.2 and is the recommended command-line parsing module in the Python standard library:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--param', dest='ParameterX', type=str, help='Defines X')
parser.add_argument('--keep_build', action='store_true')
args = parser.parse_args()

print (args.ParameterX)

if (args.keep_build): print("Keep the build directory")
else                : print("Delete the build director")

Result:

> .\test.py --param foo
foo

Ask the user for input on the command line

Will also open a command prompt window when started from the GUI/file explorer.

import sys

in_var = input("Enter a value: ")

if int(in_var) < 10:
	print("%s is less than 10" % in_var)
else:
	print("%s is equal to or more than 10" % in_var)

# Wait for ENTER. Needed to keep the cmd window open on Windows when started from GUI/with double-click.
input("Press Enter to exit...")

Running code as a script or importing code as a module (in another script).

mymodulescript.py

def func (i):
    print(i)

func("This runs whether its imported or run as a script.")

if __name__ == '__main__':
	func("This part runs only if the file is called directly (as a script).")

Format (raw) strings

Reminder: r'...' (or r"..." or R'...' or R"...") will generate raw (literal, unescaped, unmodified) text strings.

But one can still use the usual formatting helper with those:

command  = "Command foo"
argument = "-argument bar"

cli_string1 = r'{0} {1}'.format(command, argument)
cli_string2 = fr'{command} {argument}'

print(cli_string1)
print(cli_string2)

Feedback: comment@saoe.net · Categories: Development, How To · Tags: EN, Python

◀ Clear Cached Credentials from the Windows profile

Mini-Reviews #35 ▶