Python cheatsheet

Lists and dicts

Lists

Initialization

a = []
b = list()
c = ['item1', 'item2']

Clear the list:

a = []

Shuffle:

from random import shuffle
shuffle(my_list) # returns None - works in-place
print my_list

Dictionaries

Initialization

d1 = dict()
d2 = {}
d3 = {'key1': 'value1', 'key2': 123}

Obtaining dict keys

mydict.keys()

Magic methods

__nonzero__ - defining the bool value of object

__iter__ and next - object iterations

Classes

Class properties

class MyClass(object):

    def __init__():
        self._my_attr = "Default value"

    @property
    def my_attr(self):
        return self._my_attr

    @my_attr.setter
    def my_attr(self, value):
        self._my_attr = value

Static methods

class MyClass:
    @staticmethod
    def my_static_method():
        print "I am static!"
MyClass.my_static_method()
mc = MyClass()
mc.my_static_method()

Filesystem

Directories

Vytvoření adresáře:

os.mkdir()

os.path.isdir("/my/dir")

Files

os.path.isfile("/path/to/my/file.txt")

Simple listing of directory content

import os
import os.path

d = '.'
[os.path.join(d,o) for o in os.listdir(d) if os.path.isdir(os.path.join(d,o))]

Procházení adresáře - rekurzivní

os.walk - traverses into the root dir and also into all its subdirs:

import os, os.path

for root, subdirs, files in os.walk(dirname):
    for file in files:
        print "File %s has the full path: %s" % (file, os.path.join(root, file))
    for subdir in subdirs:
        print "Full subdir path is %s" % os.path.join(root, file)
        if subdir.startswith("."):
            subdirs.remove(subdir)  # do not deep into this subdir

Find the script directory

import os
print os.path.dirname(os.path.realpath(__file__))

Parse YAML file

import yaml
with open("example.yaml", 'r') as stream:
    print(yaml.load(stream))

Libraries

python -m SimpleHTTPServer