Running Python

hello.py

print('Hello, world')

Running hello.py

python hello.py

Unix/Linux

Add shebang at the beginning of the file

#!/usr/bin/python

If you don't know where is python

#!/usr/bin/env python

Make hello.py executable

chmod a+x hello.py

Numbers

Integers and Reals

>>> 2 + 2
4
>>> 53672 + 235253
288925
>>> 1 / 2 # python 3.x
0.5
>>> 9 % 3
0
>>> 2.75 % 0.5
0.25

Large numbers

>>> 1000000000000000000
1000000000000000000L
>>> 1987163987163981639186L * 198763981726391826L + 23
394976626432005567613000143784791693659L

Built-in functions

>>> pow(2, 3)
8
>>> abs(-10)
10
>>> pow
<built-in functin pow>
>>> abs
<built-in functin abs>

Conversion

>>> int(3/2)
1
>>> float(5)
5.0
>>> int
<class 'int'>
>>> float
<class 'float'>

Module math

Import math

>>> import math
>>> math.sqrt(2)
1.4142135623730951
>>> math.floor(32.9)
32
>>> math
<module 'math' (built-in)>
>>> dir(math)
['__doc__', '__name__', '__package__', 'acos', 'acosh', 'asin', 'asinh', 
 'atan', 'atan2', 'atanh', 'ceil', 'copysign', 'cos', 'cosh', 'degrees', 
 'e', 'erf', 'erfc', 'exp', 'expm1', 'fabs', 'factorial', 'floor', 
 'fmod', 'frexp', 'fsum', 'gamma', 'hypot', 'isfinite', 'isinf', 'isnan', 
 'ldexp', 'lgamma', 'log', 'log10', 'log1p', 'modf', 'pi', 'pow', 
 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh', 'trunc']

Partial import

>>> from math import sqrt
>>> sqrt(9)
3.0

But...

>>> math.sqrt(-1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: math domain error

Complex numbers

>>> import cmath
>>> cmath.sqrt(-1)
1j
>>> (1+3j) * (9+4j)
(-3+31j)

Strings

String constants

>>> "Hello, world"
'Hello, world'
>>> 'Hello, world'
'Hello, world'

Concatenating Strings

>>> 'Hello, ' 'world'
'Hello, world'
>>> "\"Hello, world!\" she said"
'"Hello, world!" she said'
>>> "Hello, " + "world!"
'Hello, world!'
>>> x = "Hello, "
>>> y = "world!"
>>> x + y
'Hello, world!'

Long Strings

print '''This is a very long string.
It continues here.
And it's not over yet.
"Hello, world!"
Still here.'''

Variables

Scope

>>> def foo(): x = 42
...
>>> x = 1
>>> foo()
>>> x
1

All is a Dictionary

>>> x = 1
>>> scope = vars()
>>> scope['x']
1
>>> scope['x'] += 1
>>> x
2

List, Tuples, Dictionaries

Accesing Values

>>> a = [1,2,3]
>>> a[1]
2
>>> a[1:2]
[2]
>>> a[-1]
3
>>> a[-1:]
[3]
>>> a[:-1]
[1, 2]

Example Method: Index

>>> knights = ['We', 'are', 'the', 'knights', 'who', 'say', 'ni']
>>> knights.index('who')
4
>>> knights.index('herring')
Traceback (innermost last):
File "<pyshell#76>", line 1, in ?
knights.index('herring')
ValueError: list.index(x): x not in list

More: dir(knights)

Dictionaries

Create a dictionary

d = {'x': 1, 'y': 2, 'z': 3}
e = dict(x=1, y=2, z=3)

Iterate

for key in d:
  print key, 'corresponds to', d[key]

Iterate keys, values

for key, value in d.items():
  print key, 'corresponds to', value

Simple Statements

Conditionals

None and False are false.

number = input('Enter a number between 1 and 10: ')
if number <= 10 and number >= 1:
  print 'Great!'
else:
  print 'Wrong!'

Loops

for

words = ['this', 'is', 'an', 'ex', 'parrot']
for word in words:
  print word

while

while True:
  word = input('Please enter a word: ')
  if not word: break
  # do something with the word:
  print 'The word was ' + word

They have break and continue

Functions

Simple

def foo():
  print("Hello, world")

Nested

def multiplier(factor):
  def multiplyByFactor(number):
    return number*factor
  return multiplyByFactor

Parameters

def print_params(x, y, z=3, *pospar, **keypar):
  print x, y, z
  print pospar
  print keypar

Classes and Objects

First Example

class Foo:
   def say(self, msg):
      print(msg)

f = Foo()
f.say('hello')

Empty Class

class Empty:
  pass

Constructors and Privacy

__init__ is invoked at beginning

Names with initial __ are private

class Dog:
  def __init__(self, name):
    self.__name = name

  def getName(self):
    return self.__name

Inheritance

class Animal:
  def __init__(self):
    print("Animal created")

class Dog(Animal):
  def __init__(self, name):
    super(Animal, self).__init__()
    self.__name = name

Modules

Modules are Programs

hello.py

def say(name):
    print("Hello,", name)

In other program or interpreter

import hello
hello.say('Adam')

from hello import say
say('Adam')

Running Modules

hello.py

def say(name):
    print("Hello,", name)

def test():
    say('World')

if __name__ == '__main__':
    test()

Searching Modules

import sys
import pprint

pprint.pprint(sys.path)

In my machine

['',
 'd:\\Python332\\lib\\site-packages\\distribute-0.6.45-py3.3.egg',
 'C:\\Windows\\SYSTEM32\\python33.zip',
 'd:\\Python332\\DLLs',
 'd:\\Python332\\lib',
 'd:\\Python332',
 'd:\\Python332\\lib\\site-packages',
 'd:\\Python332\\lib\\site-packages\\win32',
 'd:\\Python332\\lib\\site-packages\\win32\\lib',
 'd:\\Python332\\lib\\site-packages\\Pythonwin',
 'd:\\Python332\\lib\\site-packages\\setuptools-0.6c11-py3.3.egg-info']

Packages

They are directories

>>> import sqlite3
>>> sqlite3.__file__
'd:\\Python332\\lib\\sqlite3\\__init__.py'
>>> import distutils
>>> distutils.__file__
'd:\\Python332\\lib\\distutils\\__init__.py'

Metaprogramming

Creating a Class

Globals, Locals, Exec

List globals

globals()

List locals

globals()

Execute code

exec('one = 1')

See

print(exec.__doc__)

pip

A tool for installing and managing Python packages.

• https://pypi.python.org/pypi/pip
• http://www.pip-installer.org/en/latest/
• https://github.com/pypa/pip

Installing pip

See installing pip

In my Windows 8 machine:

• Install https://pypi.python.org/pypi/distribute/
• Download distribute_setup.py from http://python-distribute.org/
• Execute python distribute_setup.py
• Execute curl -O https://raw.github.com/pypa/pip/master/contrib/get-pip.py
• Execute python get-pip.py
• Add <your python>\Scripts to your path

Web Development

Flask

http://flask.pocoo.org/

Django

https://www.djangoproject.com/

• Install with pip install Django
• Run django-admin.py startproject my site
• Windows: python <pypath>\Scripts\django-admin.py startproject mysite
• cd mysite
• python manage.py runserver 8080

For database setup edit mysite/settings.py

Polls Application

Create the application with

python manage.py startapp polls

A new folder is created:

polls/
    __init__.py
    models.py
    tests.py
    views.py