Programming environments. Introduction to Python. Adrian Copie, Ph.D.

Transcription

1 Programming environments Introduction to Python Adrian Copie, Ph.D.! UVT: room 050B 1

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3 Bibliography 3 Mark Lutz - Learning Python (O Reilly) Leaning Python the Hard Way (free book) Documentation on python.org official website Any other resource on internet (there are plenty!)

4 Lecture. Table of contents. (1/2) 4 Lecture Content Lecture 1 Lecture 2 Lecture 3 Introduction to Python programming language. Advantages and disadvantages. Data types: numeric, boolean, string, lists, sets, tuples while and for loops. The name and value binding mechanism. Passing parameters to functions. Lecture 4 Lecture 5 Lecture 6 Dictionary data type. Lists and dictionaries comprehension. Files and methods of files processing. Objects comparison. Significance of True and False in Python programming language. Modules a packages in Python. Organizing programs. OOP in Python. Introduction to classes, attributes and specific methods.constructors and inheritance.

5 Lecture. Table of contents. (2/2) 5 Lecture Content Lecture 7 Lecture 8 Lecture 9 Lecture 10 Lecture 11 Lecture 12 Lecture 13 eval() function in Python and its importance. More about object creation, inheritance, composition, delegation nd other specific elements in OOP. Elements of functional programming using Python. Lambda functions, closures and decorators. Using standard exceptions in Python. Creating custom exceptions. Processes and threads in Python. Synchronization between threads. Queues. Design patterns based on Python programming language: singleton, proxy, facade, factory, adapter. Data serialization in Python, using pickle, json and databases. Elements of networking programming based on sockets and usage of urllib library. Introduction to Python s Django framework.

6 Laboratories 6 Basically we ll touch and deepen the notions and concepts discussed during the lectures.! We ll set some homework and we ll discuss it during the laboratories. We ll use Python 3.x As a recommended IDE, use PyCharm Community Edition from JetBrains (it is free)

7 Really? 7

8 Creator of Python 8

9 Python name comes from the Monty Python comedy group 9

10 Why Python? 10

11 Python Strengths Why Python? 11

12 Python Strengths Quality of the Software Why Python? 12

13 Python Strengths Quality of the Software Development Productivity Why Python? 13

14 Python Strengths Quality of the Software Development Productivity Why Python? Portability of the programs 14

15 Python Strengths Quality of the Software Development Productivity Why Python? Portability of the programs Support libraries 15

16 Python Strengths Quality of the Software Development Productivity Why Python? Component Integration Portability of the programs Support libraries 16

17 Python Strengths Quality of the Software Enjoyment Development Productivity Why Python? Component Integration Portability of the programs Support libraries 17

18 Python strengths 18

19 Python Strengths Python 19

20 Python Strengths OO Python 20

21 Python Strengths OO Free Python 21

22 Python Strengths OO Free Python Portable 22

23 Python Strengths a = 'alfa' print(type(a)) a = [1, 2] print(type(a)) OO output:! <class 'str'> <class 'list'> Python Free Portable Dynamically typed Automatic memory management Programming-in-the-large support Built-in object types Built-in tools Library utilities Third party utilities Powerful 23

24 Python Strengths OO Free Python Portable Mixable Powerful 24

25 Python Strengths OO Free Easy to use Python Portable Mixable Powerful 25

26 Python Strengths OO Easy to learn Free Easy to use Python Portable Mixable Powerful 26

27 Python Strengths 27

28 Python Downsize Being an interpreted language, is a little bit slower than C/C++ If the execution speed is the priority, use C/C++ 28

29 Python flavours 29

30 Python flavours 30 CPython Reference implementation Written in C Highest level of compatibility with Python packages and C extenstion modules PyPy Implementation in RPython (Restricted Python) Supports multiple back-ends (C, CLI, JVM) Better performance than CPython (over 5 times faster) Jython Compiles Python to Java bytecode which is eventually executed on a JVM Useful when an interface with existing Java codebase is needed IronPython Python implementation for.net framework Can be integrated directly in Visual Studio, using Python Tools for VS

31 Python In real life, usually the speed of development prevails over the speed of execution 31

32 What we can I do with Python? (I) 32

33 What can I do with Python? (II) 33 system programming (shell tools) GUIs (tkinter) internet scripting component integration database programming rapid prototyping numeric and scientific programming games image processing robots many more

34 Python vs. Java 34

35 Comparison Java vs. Python (I) 35 Java Python public class Main { public static void main(string[] args) { System.out.println(" hello world"); } } print "hello world"; public static void main(string[] args) { String test = "compare Java with Python"; for(string a : test.split(" ")) a="compare Python with Java"; print a.split(); System.out.print(a);

36 Comparison Java vs. Python (II) Java class Animal{ private String name; public Animal(String name){ this.name = name; } public void saysomething(){ System.out.println("I am " + name); } } class Dog extends Animal{ public Dog(String name) { super(name); } public void saysomething(){ System.out.println("I can bark"); } } public class Main { public static void main(string[] args) { Dog dog = new Dog("Chihuahua"); dog.saysomething(); class Animal(): Python def init (self, name): self.name = name def saysomething(self): print "I am " + self.name class Dog(Animal): def saysomething(self): print "I am "+ self.name \ + ", and I can bark" dog = Dog("Chihuahua") dog.saysomething() } } 36

37 Comparison Java vs. Python (III) Java File dir = new File(".");// get current directory File fin = new File(dir.getCanonicalPath() + File.separator + "example.txt"); FileInputStream fis = new FileInputStream(fin); // //Construct the BufferedReader object BufferedReader in = new BufferedReader(new InputStreamReader(fis)); String aline = null; while ((aline = in.readline())!= null) { // //Process each line, here we count empty lines if (aline.trim().length() == 0) { } } // do not forget to close the buffer reader in.close(); Python myfile = open("/home/student/programs/example.txt") print myfile.read(); 37

38 Coding Style! It is important to follow consistency and obey a coding style PEP (Python Enhancement Proposal) PEP8 38

39 Python does not have code blocks 39

40 Python Philosophy 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! 40

41 Python Interpreter (Image from 41

42 Python shell 42

43 Python IDE (PyCharm) 43

44 Structure of Python programs Python Program Module 1 Module 2 Module 3 Module n Python Module Statement 1 Statement 2 Statement 3 Statement n Python Statement Expression 1 Expression 2 Expression 3 Expression n Python Expression Object 1 Object 2 Object 3 Object n 44

45 Python built-in objects 45 Object type Example Numbers Strings 123, , Decimal abc, spam, b x\01c Lists [1, [2, three ], 4] Dictionaries { language : python, version : 3 } Tuples (1, two, 3, IV ) Files f = open( python, r ) Sets set( abc ), { a, b, c } Other Boolean, None

46 46 Numbers Integers (123, 99) Floating point (1.23, 0.99) Complex (1j, 1+2j) Fixed precision decimals Rational fractions (Fraction(2,3))

47 47 Number operators Operator Operation + addition * multiplication - subtraction / division ** exponentiation % modulus // floor division

48 Booleans 48 Booleans - represents the truth value of an expression In Python: {True, False} Operations: not, and, or x y not x not y x and y x or y True! False! False! False! True! True! True! False! False! True! False! True! False! True! True! False! False! True! False! False! True! True! False! False!

49 Strings 49

50 Strings - Definitions 50 Strings: Record textual information Record arbitrary collection of bytes Represent a so called sequence Sequences: positionally ordered collection of other objects maintain a left-to-right order among the items they contain: their items are stored and fetched by their relative position

51 51 Sequences - Operations (I) Length of a string >>>s = python >>>len(s) 6 Indexing sequences >>>s[0] p >>>s[-1] n >>>s[-2] o

52 52 Sequences - Operations (II) Slicing >>>s[1:3] yt! >>>s[1:] ython! >>>s[:3] pyt! >>>s[:] python

53 53 Sequences - Operations (III) Concatenation >>> monty + s monty python Repetition >>>s * 3 pythonpythonpython

54 Strings - Immutability 54 Strings are immutable. Every string operation produces a new string. >>> s= python'! >>> s[0] p'! >>> s[0]='b' Traceback (most recent call last): File "<input>", line 1, in <module> TypeError: 'str' object does not support item assignment

55 Strings are immutable 55 s = 'alfa' print(id(s)) s = 'beta' print(id(s)) output:! One can notice that after reassigning of a new value, the s object is recreated, receiving a new id

56 56 Strings - Some useful methods find >>> s.find('on') 4 replace >>> s.replace('p', 'j') 'jython' split >>> s='cython,jython,python' >>> s.split(',') ['cython', 'jython', 'python']

57 Strings - Getting help (I) 57 >>>dir(s)! [' add ', ' class ', ' contains ', ' delattr ', ' dir ', ' doc ', ' eq ', ' format ', ' ge ', ' getattribute ', ' getitem ', ' getnewargs ', ' gt ', ' hash ', ' init ', ' iter ', ' le ', ' len ', ' lt ', ' mod ', ' mul ', ' ne ', ' new ', ' reduce ', ' reduce_ex ', ' repr ', ' rmod ', ' rmul ', ' setattr ', ' sizeof ', ' str ', ' subclasshook ', 'capitalize', 'casefold', 'center', 'count', 'encode', 'endswith', 'expandtabs', 'find', 'format', 'format_map', 'index', 'isalnum', 'isalpha', 'isdecimal', 'isdigit', 'isidentifier', 'islower', 'isnumeric', 'isprintable', 'isspace', 'istitle', 'isupper', 'join', 'ljust', 'lower', 'lstrip', 'maketrans', 'partition', 'replace', 'rfind', 'rindex', 'rjust', 'rpartition', 'rsplit', 'rstrip', 'split', 'splitlines', 'startswith', 'strip', 'swapcase', 'title', 'translate', 'upper', 'zfill']

58 Strings - Getting help (II) 58 >>> help(s.format)! Help on built-in function format:! format(...) method of builtins.str instance S.format(*args, **kwargs) -> str Return a formatted version of S, using substitutions from args and kwargs. The substitutions are identified by braces ('{' and '}').

59 Conclusions Strengths: OO, Free, Portable, Powerful, Mixable, Easy to Use, Easy to Learn Weaknesses: A little bit slower than other compiled languages Interpreted language Use: for a wide area of projects, general purpose language 59

60 End of Lecture 1 60