Python

Ko-Lung Yuan

Why Python?

• • • • • • • • • Simple and elegant Good readability Object-oriented / dynamic(script) language High productivity Abundant resources(libraries…) Active community Wide range of uses Embeddable and Extendibility Interactive Learning / well document

Python’s history • http://zh.wikipedia.org/wiki/Python Guido van Rossum

Zen of Python • • • • • • • • • • • • • • • • • • • Beautiful is better than ugly.

Explicit is better than implicit.

Simple is better than complex.

Complex is better than complicated.

Flat is better than nested.

Sparse is better than dense.

Readability counts.

Special cases aren't special enough to break the rules.

Although practicality beats purity.

Errors should never pass silently.

Unless explicitly silenced.

In the face of ambiguity, refuse the temptation to guess.

There should be one-- and preferably only one --obvious way to do it.

Although that way may not be obvious at first unless you're Dutch.

Now is better than never.

Although never is often better than *right* now.

If the implementation is hard to explain, it's a bad idea.

If the implementation is easy to explain, it may be a good idea.

Namespaces are one honking great idea -- let's do more of those!

Python之禪 • • • • • • • • • • • • 美麗優於醜陋，明講好過暗諭。 簡潔者為上，複雜者次之，繁澀者為下。 平舖善於層疊，勻散勝過稠密；以致輕鬆易讀。 特例難免但不可打破原則，務求純淨卻不可不切實際。 斷勿使錯誤靜靜流逝，除非有意如此。 在模擬兩可之間，拒絕猜測的誘惑。 總會有一種明確的寫法，最好也只有一種， 但或須細想方可得。 凡事雖應三思後行，但坐而言不如起而行。 難以解釋的實作方式，必定是壞方法。 容易解釋的實作方式，可能是好主意。 命名空間讚，吾人多實用。

蟒之道 • • • • • • • • • 妍優於寢 喻莫如敘 是故簡勝繁 繁勝亂 平舖勝汲營 綿密不如疏俊 唯平易而已 無例外於其例 不獨清於實際 毋默於誤 其惡非務 寧戚戚於尋徑 勿揣揣於模稜 道謀於一 可以得矣 力行者宜立行於當下 利行者長三思而後行 不可說之說不可說 可以道之道可以道 名域鳴於域 可取

How to Get Python • Official website: http://www.python.org/

Install Python • Python Interpreter and Libraries •

Linux

: sudo apt-get install python3.1-dev

IDLE • A basic but useful editor for Python • • • • Text-Indent Keyword-Highlight Interactive interface Easy to test code

First, We should know… • • • • No semicolon (

;

No brace (

{ }

Using colon (

:

) ) Using text-Indent ) X X O O

Comment • Single-line comment (

#

)

# This is an example of single-line comment

• Multi-line comment (

“”” “””

)

“””This is an example of multi-line comment You can write the comment in several lines”””

Variable • Build variable (

Var = …

Var = 70 Var = 6.78

Var = “alcom lab”

) • • •

No declaration

but

definition Naming Rule

and

type

No need to worry about where the variables and their sizes,

all of the details are hided !

Input and Output • Output (

print()

)

print(100) print(“a=”,a)

• Input (

raw_input(

[hint]

)

)

raw_input(“name:”)

String • • • Using quote (

‘ ’

,

“ ”

,

“”” ”””

)

s1=‘apple’ s2=“banana” s3=“””I love you””” print(s1,s2,s3)

Strings are unchanged object Using

escape characters(e.g. /n)

String Operation • Concatenate(

+

)

“alcom”+”lab”

• Repeat(

*n

)

“go”*3

• Length(

len()

)

len(“three”)

• • Exist(

in

)

‘a’ in ‘apple’

Split(

.split(“string”)

)

“abc cde”.split(“ ”)

Mathematic Type • • • Integer - no limit

123123123112432532643877698709760909

Float – Not exact, support science notation

123.456

1.2e-3 Complex number 1+2j 1.23+34.7+5j

Mathematic Operation • • • Basic operation

+ - * / %

Floating Point –

base on simple one 10/3 50*0.5

10+3j-3j

Special operation

** // 16**0.5

10.0//3.0

All things in python are objects!

List • • • • • An ordered data structure (Like array) Mutable Sequence

[object 1, object 2, …] listex = [1, 2.34, ”alcom”, 7+8j]

Support Nested List

nestlist = [ [1,2,3] , [4.2, “john”], Var]

Access method

listex[-1] nestlist[0][2]

• • • • • • • • • • Length Append Extend Count Index Insert Pop Remove Reverse Sort List Operation

len(nestlist) listex.append(20) listex.extend([2,3,4]) [1,1,2,3].count(1) [1,1,2,3].index(1) [1,1,2,3].insert(1,1) [1,1,2,3].pop() [1,1,2,3].remove() [1,2,3,4].reverse() [1,2,3,4].sort()

Dictionary • • • Dictionary is a mapping object

Key



value D = { key1:value1, key2:value2, …} D[key] = value D[key]

Dictionary is unordered

Set

is another unordered data structure

•

S[ i ]

•

S[ i : j ]

• •

S[ i : j : k ]

Some examples Slice

if condition: … elif condition: … else: … PS : Text-Indent!!

If else

Logical Operation • • • • • • • == != < > <= >= Or And Not Boolean value:

True False

For Loop

For Var in container : …code… …code… For Var in range(x) : …code… …code…

Container • • • • • • Container are the iterative objects

List

: elements of list

Dictionary

: keys of dictionary

Tuple

: elements of tuple

File

: lines of file

range(x)

: build a list

[0, 1, 2, … ,x-1]

In and List Comprehension •

In

is an useful keyword 1. in relation 2. for iteration

if a in “abc” for a in list:

•

List Comprehension

List = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] List2 = [item*10

for

item

in

List]

While Loop

While

condition: …code…

While True

: …code…

Nested Structure • • • • We can use nested structure in python For loop While loop If elif else

Build-in Function • Length:

len()

• Sort:

sorted()

V.s. object.sort()

Function Factory • Change object type!

•

int( )

•

str( )

•

float( )

Module / Import / Namespace • • • A .py file is a module whose name is same as the file name Use module by import

import sys

Every module has a namespace of its own – Original-> (main) – Import one-> It’s name

User Function •

def

funciton_name(parameters[=default value]): …function description… • Call function

namespace.function_name(parameters) namespace.function_name(parameters, appointed parameter1=value, appointed parameter2=value, …)

Other important issues • • • • • User Object File IO (simple demo) Exception Handling Pypi pickle

Strong Python • • • • • APPs Website(server program) Linux Shell Script / Linux Managing Latex Combine with C/C++

Python with Linux (1/2) • • • • • • • •

#!/usr/bin/python # -*- coding: UTF-8 -* Import os

and

shutil

os.unlink('data.new.txt') os.rename('data.txt', 'data.alter.txt') shutil.copy('data.txt', 'data.new.txt') shutil.move('data.alter.txt', 'data.txt')

chmod a+x python-script-file

Python with Linux (2/2) • • Run outer program

os.system(“program”)

Pipeline and get the return value

import popen2 stdout, stdin = popen2.popen2(“ls”) ostr = stdout.read() print(ostr)

Python with C/C++ • http://docs.python.org/extending/extending.

html

Python with Latex • http://www.texample.net/weblog/2008/oct/2 4/embedding-python-latex/

Useful Books • • • • • Head First Python Dive into Python Programming in Python3 Python Essential Reference Learning Python

Useful Websites • • • • http://ez2learn.com/index.php/python tutorials http://wiki.python.org.tw/ http://caterpillar.onlyfun.net/Gossip/Python/i ndex.html

http://pypi.python.org/pypi