On Python language How to use Python Syntax of Python Types in Python...

On Python languageHow to use Python

Syntax of PythonTypes in Python

Outline

1 On Python language

2 How to use Python

3 Syntax of Python

4 Types in PythonSimple types in PythonCollectionsProcessing collectionsStringsTips

Marcin Młotkowski Object–oriented programming 1 / 52



The beginnings of Pythons

90 — CWI Amsterdam, Guido van Rossum




Current state

Python Software Foundation (PSF)




Current version

2.* (2.4, 2.6, 2.7.2)

3.* (3.2.2)




Why I like Python

Simple and clean syntax:

few keywords and operators;

indentation is obligatory

factorial

def fact(x):if x == 0:

return 1else :

return x * fact(x-1)




Why Python is so cool

Styles of programming

structural programming

object–oriented programming

functional programming





Built-in types

Lists

vec = [1, 2, 3]doubled_vec = [ 2*e for e in vec]

Dictionaries

phone = { ’chris’ : 235711, ’Susie’ : 246810 }print tel[’susie’]





Batteries included

I/O libraries

regular expressions

HTTP, HTML, XML

GUIs: pyGTK, wxPython, Tkinter, PythonWin

...

...




Other features of Python

Dynamic type system

>>> 2 + "two"Traceback (most recent call last):File "<stdin>", line 1, in ?

TypeError: unsupported operand type(s) for +: ’int’and ’str’>>>




Applications of Python

Projects

System tools (RedHat)

Google

NASA

ZOPE/PLONE

http://www.python.org/about/success/




Outline


2 How to use Python

3 Syntax of Python





Interactive mode

$ python>>> 2+24>>> [1,2,3][-1:][3]Ctrl-d$




Execute a file

$ python a_file.py

What’s happened

1 program compilation (inc. syntax checking)

2 sometimes a file *.pyc is created

3 execute a program




Outline


2 How to use Python

3 Syntax of Python





Syntax

Assignment

four = 2 + 2x = y = z = 0name = ’Pyt’ + ’hon’primes = [2, 3, 5, 7]a, b = b, a+b




Syntax

Conditional statement

x = 4if x % 2 == 0:print "even"print "x = ", 2

x = 4if x % 2 == 0:print "even"

print "x = ", 2




Syntax

Conditional statement

x = 400if x % 2 == 0:if x > 100: print "large even"elif 10 < x <= 100:print "small even"

else:print "tiny even"




Logic expressions

false: 0, False, None, [],

true: True, nonempty values

conjunctions: and, or, not

operators: ==, !=, 1 < x < 2




Loop statement

A statement while

a, b = 0, 1while b < 10:print ba, b = b, a + b




Loop statement

for in

a = [1,2,3,4]for e in a:print e

print "end"




Loop statements

for in

sum = 0for i in range(100):sum = sum + i

print "sum=", sum




Other statements

break and continue

empty statement: pass

while (True): pass




Functions

def foo(arg1, arg2=1, arg3=[3]):print arg1, arg2, arg3return 4

foo("one", 2)print foo(1, 2, 3)




Comments

def fun (arg):""" This is very important functionUse with high esteem"""

# end if empty argumentif arg == None: returnreturn arg




Input/output

Python 2.*

print "Hello world"x = input("Type x: ")y = input("Type y: ")print "x =", x, " y =", y

Python 3.0

print("Hello world")x = input("Type x: ")y = input("Type y: ")print("x =", x, " y =", y)




Tips

Editors with syntax highlighting: vim, gedit, emacs

Tools

idlePythonCard/codeEditor

"Executable"files and national characters:

file.py

#!/usr/bin/python# -*- coding: iso-8859-2 -*-




Why "Python"?




Further reading

www.python.org

"Dive into Python", Mark Pilgrim

...




Simple types in PythonCollectionsProcessing collectionsStringsTips

Outline


2 How to use Python

3 Syntax of Python






Simple types

simple types: integers, floats, booleans

sequential types: strings, lists, tuples





”Simple” integers

Range: [−sys.maxint − 1, sys.maxint]

Operators: +, - , /, //, %, **

Standard functions: abs(x), divmod(x, y) = (x // y, x % y)

Warning

Dividing integer by integer gives integer

4//3 = 1





Integers and conversions

(1.0 ∗ 4)//3 = 1.0

(1.0 ∗ 4)/3 = 1.33333333333333

float(4)/3 = 4/float(3)





Large integers

Example

>>> 1000 ** 101000000000000000000000000000000L>>> long(100)100L





Constants

Integers0x123, 0x123456789L, 0123, 06789L

Floats3.14 10. .002 .271e1





Complex numbers

Literals and expressions1 + 3jx + 12jcomplex(x,0)

Operatorsx.real ∗ ∗2 + y.imag ∗ ∗2





Standard numerical libraries

math

import mathprint math.cos(3.14)

random

from random import *print random()





Examples

Lists: [12,3]

Strings: "abc", ’def’, u’Zazółc zółta jazn’

tuples: (1, ”one”, (1, 2+3j, 0x4))

dictionaries

Sets





Tuple

brown = 165, 42, 42NavyBlue = (0,0,128)htmlColor = { ’turquoise’ : (64,224,208), ’NavyBlue’ :NavyBlue }r, g, b = htmlCol[’NavyBlue’]





Reminder

assignment

(

a, b

)

=

(

1, 2

)





Reminder

assignment

(a, b)= (1, 2)





Inclusion operator

in

’bc’ in ’abcd’4 not in [2, 3, 5, 7, 11]’pi’ in { ’pi’ : 3.1415, ’e’ : 2.7182 }





Collection operators

+

>>> [ ’one’, 2, 3.0 ] + [ 0x4, 05 ][’one’, 2, 3.0, 4, 5]>>> (’one’, 2, 3.0) + (0x4, 05)(’one’, 2, 3.0, 4, 5)





Size of collection

len

len( [’one’, 2, 3.0] )len( {’one’ : 1, ’two’ : 2 } )len( (1, 2, 3) )





Elements of collections

[1, 2, 3][2] = 3

’abcd’[1:3] = ’bc’(1, 2, 3)[1:] = (2, 3)(1,2,3)[:1] = (1, )’Python’[:-1] = ’Pytho’’Python’[-1:] = ’Python’[-1] = ’n’






[1, 2, 3][2] = 3’abcd’[1:3] = ’bc’

(1, 2, 3)[1:] = (2, 3)(1,2,3)[:1] = (1, )’Python’[:-1] = ’Pytho’’Python’[-1:] = ’Python’[-1] = ’n’






[1, 2, 3][2] = 3’abcd’[1:3] = ’bc’(1, 2, 3)[1:] = (2, 3)

(1,2,3)[:1] = (1, )’Python’[:-1] = ’Pytho’’Python’[-1:] = ’Python’[-1] = ’n’






[1, 2, 3][2] = 3’abcd’[1:3] = ’bc’(1, 2, 3)[1:] = (2, 3)(1,2,3)[:1] = (1, )

’Python’[:-1] = ’Pytho’’Python’[-1:] = ’Python’[-1] = ’n’






[1, 2, 3][2] = 3’abcd’[1:3] = ’bc’(1, 2, 3)[1:] = (2, 3)(1,2,3)[:1] = (1, )’Python’[:-1] = ’Pytho’

’Python’[-1:] = ’Python’[-1] = ’n’






[1, 2, 3][2] = 3’abcd’[1:3] = ’bc’(1, 2, 3)[1:] = (2, 3)(1,2,3)[:1] = (1, )’Python’[:-1] = ’Pytho’’Python’[-1:] = ’Python’[-1] = ’n’





Slicing

>>> ’informatics’[::3]’ioac’





Iterations over collections

x = [1,2,3]y = [4,5,6]prod = 0for i in range(len(x)):

prod += x[i] * y[i]





List processing

x = [1,2,3]y = [4,5,6]prod = 0for i, v in enumerate(x):

prod += v * y[i]print prod





List processing, other implementation

x = [1,2,3]y = [4,5,6]prod = 0for a, b in zip(x, y):

prod += a * bprint prod





Dictionary processing

iteration

dict = { ’uno’ : 1, ’duo’ : 2, ’tre’: 3 }for key, val in dict.iteritems():

print key, "=", val





Constants

’Alice has a cat’“Alice has a cat”

Unicode

uZazółc zółta jazn""Zazółc zółta jazn"

Unicode

len(u"zółty") == 5len("zółty") == 8

Long strings

"""This is amultiline string""""





Strings

Strings are collections

’raw’ strings: r’abcd\n’

String continuation:"This is a \n\very long string\n"

A lot of library functions

Strings are immutable, ie. ’abc’[1] = ’d’





String formatting

Operator %

print "%i + %i = %i\n" % (2, 2, 2+2)

dict = { ’two’ : 2, ’four’ : 4 }print "%(two)s + %(two)s = %(four)s\n" % dict





First aid

Interactive mode

>>> type(3.1415)<type ’float’>>>> dir(float)....>>> dir(3.1415)....>>> float.__doc__


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