Python
Python is a widely used general-purpose, high-level programming language. Its design philosophy emphasizes code readability, and its syntax allows programmers to express concepts in fewer lines of code than would be possible in languages such as C. (Wikipedia)
Contents
Setup
Installation
Ubuntu/Debian
Install Python (and for developing may also python-dev
)
sudo apt-get install python
- Install old version 2.6
sudo add-apt-repository ppa:fkrull/deadsnakes
sudo apt-get update
sudo apt-get install python2.6
Windows
Download the Python Windows installer and follow the introductions to install it
- Execute Pythin in command line
The installer asks you to add path to your system path. Anyway, if you want to do it manually, expand the system variable PATH
by adding (the second path it not necessary need): C:\Python27
, C:\Python27\Scripts
pip
pip is a tool for installing and managing Python packages.
Installation
- Ubuntu:
sudo apt-get install python-pip
(for Python 3 usepython3-pip
instead) - Windows: Download the get-pip.py file and execute it in the command line:
python get-pip.py
Basic usage
Install a package or a specific version of a package
pip install <package-name>
pip install <package-name>==1.8.5
pip install <package-name>==1.8.*
Create a requirements file and install the requirements
pip freeze [--local] > requirements.txt
pip install -r requirements.txt
List packages
pip list
Advanced usage
Upgrade pip itself
pip install -U pip
Remove all git packages
pip freeze | xargs pip uninstall -y
virtualenv
Install virtualenv
virtualenv creates isolated Python environments.
pip install virtualenv
Usage
(1) Create the environment example_env, (2) activate, (3) install a Python package with pip (and (4) deactivate it)
virtualenv example_env
source example_env/bin/activate
pip install <package-name>
deactivate
In this environment you can normally run pip install <package>
.
Specify Python version
Create an environment with a specific Python version
virtualenv --python python2.7 example_env
virtualenv --python /usr/bin/python2.7 example_env
Basics
Variables
example = 6
example = 'Hello'
example = float(6.0)
example = float('inf') # infinity
example = int(6)
Condition
if example > 6:
print 'if'
elif example is '6':
print 'elif'
else:
print 'else'
Loops
For loop
for i in range(0, 3):
print 'index %d' % (x)
While loop
start = 0
while start <= 5:
print start
start += 1
Function
def myFunction(param1, param2):
print param1
return param2
Set
# unordered set
example = {20, 5, 31}
# ordered set
example = [20, 5, 31]
example = ['hello', 'world']
Advanced
Run a script
Create a file named myScript.py
#!/usr/bin/env python
# -*- coding: utf-8 -*-
print 'Hello world'
Run the file
python myScript.py
Main method and arguments
if __name__ == '__main__':
argv = sys.argv[1:]
if len(argv) == 1:
print('filename: {}'.format(argv[0]))
else:
print('Usage: example.py <FILENAME>')
Class
class MyClass:
TYPE = 'Hello'
def __init__(self, type):
if type != self.TYPE:
raise Exception('Unkown type!')
self.type = type
def myFunction(self, param):
print(self.type)
print(param)
return
MyClass('Hello').myFunction('World')
- Inherit class
class Car:
def myFunction(self, type):
print("Hi")
class Audi(Car):
def myFunction(self, type):
print("World")
More
Code style
PEP 8 is a style guide for Python. You can check your code against this style convention by using the tool pep8 (documentation). In the Eclipse plugin PyDev is pep8 already include:
- Window > Preferences
- PyDev > Editor > Code Analysis
- pep8.py
Problems and errors
IOError: Could not build the egg
- Error message
IOError: Could not build the egg.
- Solution[1]
pip install mysql-python