Introduction to Python. Didzis Gosko

Transcription

1 Introduction to Python Didzis Gosko

2 Scripting language From Wikipedia: A scripting language or script language is a programming language that supports scripts, programs written for a special run-time environment that can interpret (rather than compile) and automate the execution of tasks that could alternatively be executed one-by-one by a human operator*.... The term "scripting language" is also used loosely to refer to dynamic high-level general-purpose language, such as Perl, Tcl, and Python, with the term "script" often used for small programs (up to a few thousand lines of code) in such languages... * Python has interactive shell

3 Shell Scripting (bash etc.) vs Python Shell Scripting (bash etc.): + Shell scripting has simpler notations for I/O redirection. + It is simpler to create pipelines out of existing programs in shell. +/- Ugly syntax of control flow statements - Most of tasks (any data processing) are delegated to external programs (awk, sed, perl, python etc.) - Extensive use of process forking - Compatibility problems between platforms Python: + General purpose programming language + Easy (elegant) syntax + Complete toolset in a monolith package + Cross-platform + Powerful +/- Block indentation - I/O redirection, creating pipelines etc. not as easy as with Shell Scripting - Not all systems have python installed (it s also true with bash)

4 Bash vs Python #!/bin/bash # comment line echo "what a fine day: " date Output, when called by./test.sh : what a fine day: Thu Oct 28 23:37:39 EEST 2004 #!/usr/bin/env python3 # comment line print("what a fine day:") import os os.system("date") Output, when called by «./test.py»: what a fine day: Thu Oct 28 23:37:39 EEST 2004

5 Each task has it s own tool Shell Scripting: program execution, input/output capturing and chaining (with pipes). Python: file content/data processing (from perspective of shell scripting) any other task... can be used as scripting language (unlike C/C++, Java etc.) In general Python doesn t compare with Shell Scripting.

6 Python is good for Concept checking Fast prototyping Any performance non-essential programming task String processing A readable, dynamic, pleasant, flexible, fast and powerful language

7 Overview Background Syntax Types / Operators / Control Flow Functions Classes Tools

8 What is Python Multi-purpose (Web, GUI, Scripting, etc.) Object Oriented Interpreted Strongly typed and Dynamically typed Focus on readability and productivity

9 Features Batteries Included Everything is an Object Interactive Shell Strong Introspection Cross Platform CPython, Jython, IronPython, PyPy

10 Who Uses Python Google NASA Yahoo Gentoo Linux...

11 Releases Created in 1989 by Guido Van Rossum Python 1.0 released in 1994 Python 2.0 released in 2000 Python 3.0 released in 2008 Python 2.7 is the last version of Python 2 Python 3.4 is the latest version

12 Syntax

13 Hello World hello_world.py

14 Indentation Most languages don t care about indentation Most humans do We tend to group similar things together

15 Indentation The else here actually belongs to the 2nd if statement

16 Indentation The else here actually belongs to the 2nd if statement

17 Indentation Some do like this

18 Indentation You should always be explicit

19 Indentation Text Python embraces indentation

20 Comments

21 Types

22 Strings

23 Numbers

24 Null

25 Lists

26 Lists

27 Dictionaries

28 Dictionary Methods

29 Booleans

30 Operators

31 Arithmetic

32 String Manipulation

33 Logical Comparison

34 Identity Comparison

35 Arithmetic Comparison

36 Control Flow

37 Conditionals

38 For Loop

39 Expanded For Loop

40 While Loop

41 List Comprehensions Useful for replacing simple for-loops.

42 Functions

43 Basic Function

44 Function Arguments

45 Arbitrary Arguments

46 Fibonacci

47 Fibonacci Generator

48 Classes

49 Class Declaration

50 Class Attributes Attributes assigned at class declaration should always be immutable

51 Class Methods

52 Class Instantiation & Attribute Access

53 Class Inheritance

54 Python s Way No interfaces No real private attributes/functions Private attributes start (but do not end) with double underscores. Special class methods start and end with double underscores. init, doc, cmp, str

55 Imports Allows code isolation and re-use Adds references to variables/classes/functions/etc. into current namespace

56 Imports

57 More Imports

58 Error Handling

59 Documentation

60 Docstrings

61 Tools

62 IPython ( better interactive shell and more Continuum Analytics Anaconda Python distribution ( CPython Jython IronPython PyPy Cython

63 SciPy NumPy Matplotlib Sympy pandas scikit-learn IPython

64 Web Frameworks Django Flask Bottle.py Twisted...

65 IDEs Emacs Vim Komodo PyCharm Eclipse (PyDev)

66 Package Management

67 Resources

68 Example

69 Going Further Decorators Context Managers Lambda functions Generators...

70 Other Scripting options Ruby Perl JavaScript (Node.js) TypeScript (compiles to JavaScript) CoffeeScript (compiles to JavaScript) PHP...

71 Glue languages Erlang Unix Shell scripts (ksh, csh, bash, sh and others) Windows PowerShell ecl DCL Scheme JCL m4 VBScript JScript and JavaScript AppleScript Python Ruby Lua Tcl Perl PHP Pure Rexx XSLT