Python
Contents
About
Python is a highly popular high-level programming language with a focus on code readability and minimal lines of code. Unlike most languages that use braces (C++, Java, etc.), python uses indentation to create code blocks (inside conditional statements and loops).
I've only done a small amount in Python when I started this page, but I aimed for competency/readability soon. Until then, I'll document useful pieces of code I write here.
Child Pages
Related/Child Pages:
- General:
- Python Constructs - some constructs in the python language I forget.
- Python Cheatsheet - an amazing python cheatsheet.
- Example code:
- Python - ncurses printing html as colors - more work with ncurses.
- Python - HTML scraper - how to scrape web pages with python.
- Python - regex example - basic regex examples.
- Python - thread examples - basic thread examples.
- Python - libraries - 3rd party libraries like `matplotlib`.
- Python - testing - how to test python code with `unittest`.
- Python - servers - some popular REST server libraries in python.
- Programming Questions:
- Programming question - Bowling Score - a fun programming question.
- Programming question - Boggle - another fun programming question.
- Misc:
- Unix - Python script - print file with color scheme - a little program I wrote which inputs a text file (in this case HTML) and replaces certain tags with ANSI color codes to produce colored output to the terminal.
- Ncurses ui - shows how to build a simple ncurses interface using Python.
- Cinema 4D - Python scripts - a bunch of scripts I wrote for Cinema 4D in Python.
Installing Python
Before you can create a Hello World, you must install Python. Visit the python.org website to download and install the latest version of python.
Each OS should have an installer... for Windows for example I followed the latest version and used the "Windows x86-64 executable installer" (python-3.5.0-amd64.exe) link.... and by ticking the "add to PATH" option you can then run "cmd" and type "python program_name.py".
| Warning: There are some significant differences between python 2.7 and python 3.x.... some of the code below may need adjusting depending which version you downloaded |
Creating a Hello World in Python
To execute a python program, install python (instructions above) then create a text file with a .py extension like the following:
hello_world.py:
print ("Hello, World!")Now start a new Terminal and run:
$ python hello_world.py
Although this hello world example works fine, a good practice is make the file executable on it's own. Change "hello_world.py" to:
#!/usr/bin/env python
print ("Hello again, World!")The #!/usr/bin/env python line tells it to add python to the front if directly executed. The following two commands make it executable and then execute it:
$ chmod a+x hello_world.py $ ./hello_world.py
Python Templates
Hello World
def hello_world():
"""Function that prints hello world."""
print ('Hello World')
if __name__ == '__main__':
hello_world()Python Bare Bones Command Line Program With Arguments
Good practice is to have a "def main()". The following example includes a main, and also demonstrates the 'optparse' for parsing arguments.
simple_program_with_args.py:
#!/usr/bin/env python
# simple_program_with_args.py - command line program which inputs a
# name '-f Andrew' and prints a hello message to that name.
import optparse
usage_str = 'Usage: python simple_program_with_args.py -name Andrew'
def main():
p = optparse.OptionParser()
p.add_option('--name', '-n', default='World')
options, arguments = p.parse_args()
contents = usage_str;
if options.name != 'World':
contents = 'Hello ' + options.name;
print (contents + '\n')
if __name__ == '__main__':
main()Basic File Read/Write
File operations usually look like: f = open("file.txt","w",encoding="utf8") ... where r = read, w = write, a = append.... do one of: read, readlines, readline, write, writelines.... and then don't forget to f.close()... unless you've used with, then you don't need to call close:
simple_file_read_then_write.py:
# Open the file for reading and store its content:
with open("input.txt", "r") as file:
content = file.read()
# Open the file for writing and update its content:
with open("input.txt", "w", encoding="utf8") as file:
file.write(content + "\nTHE END")To read line by line you can also do:
f = open('input.txt', 'r', encoding='ascii')
for line in f:
print(line, end='')
f.close()
Basic Console Input
Yup, just use input() to prompt input on the console:
simple_input_prompt.py:
print('What is your name?') # ask for their name
my_name = input()
print('Hi, {}'.format(my_name))
Cheatsheet
