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Python-01| Fundamentals
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  1. 1. Python Session 1– Introduction Dr. Wessam M. Kollab
  2. 2. What is Python?  Python is a general-purpose interpreted, interactive, object-oriented, and high- level programming language. It was created by Guido van Rossum during 1985- 1990.  It is used for: • web development (server-side). • software development. • Mathematics. • GUI applications. • Scrape data from websites. • Analyze Data. • Game Development. • Data Science
  3. 3. Why Python?  Python is an interpreted language when you run python program an interpreter will parse python program line by line basis, as compared to compiled languages like C or C++, where compiler first compiles the program and then start running. interpreted languages are a little slow as compared to compiled languages.  Python is Dynamically Typed Python doesn't require you to define variable data type ahead of time. Python automatically infers the data type of the variable based on the type of value it contains. myvar = "Hello Python" The above line of code assigns string "Hello Python" to the variable myvar, so the type of myvar is string. myvar = 1 Now myvar variable is of type int.
  4. 4. Why Python?  Python is strongly typed If you have programmed in PHP or javascript. You may have noticed that they both convert data of one type to another automatically. In JavaScript 1 + "2" will be ’12’ Here, before addition (+) is carried out, 1 will be converted to a string and concatenated to "2", which results in '12', which is a string. However, In Python, such automatic conversions are not allowed, so 1 + "2" will produce an error.
  5. 5. Why Python?  Write less code and do more Programs written in Python are usually 1/3 or 1/5 of the Java code. It means we can write less code in Python to achieve the same thing as in Java. To read a file in Python you only need 2 lines of code: with ("myfile.txt") as f: print(f.read())  Python works on different platforms (Windows, Mac, Linux, etc).
  6. 6. Why Python?  The fastest-growing major programming language, as you can see in Figure 1-4.
  7. 7. Python Syntax compared to other programming languages  Python was designed for readability, and has some similarities to the English language with influence from mathematics.  Python uses new lines to complete a command, as opposed to other programming languages which often use semicolons or parentheses.  Python relies on indentation, using whitespace, to define scope; such as the scope of loops, functions and classes. Other programming languages often use curly-brackets for this purpose.
  8. 8. Data: Types, Values, Variables, and Names Python Data Are Objects  Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.  Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals or characters in these variables.  Assigning Values to Variables Python variables do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable. counter = 100 # An integer assignment miles = 1000.0 # A floating point name = "John" # A string
  9. 9. Data: Types, Values, Variables, and Names Python variable names have some rules:  They can contain only these characters:  Lowercase letters (a through z)  Uppercase letters (A through Z)  Digits (0 through 9)  Underscore (_)  They are case-sensitive: thing, Thing, and THING are different names.  They must begin with a letter or an underscore, not a digit.  They cannot be one of Python’s reserved words (also known as keywords). >>> help("keywords") >>> import keyword >>> keyword.kwlist
  10. 10. Data: Types, Values, Variables, and Names Variables Are Names, Not Places In Python, if you want to know the type of variable, you can use type(variable Name) >>> type(7) <class 'int’> Assigning to Multiple Names >>> a = b = c = 2 >>> a = b = c = 1,2,”Ahmed” Reassigning a Name Because names point to objects, changing the value assigned to a name just makes the name point to a new object. Copying As you saw in Figure 2-4, assigning an existing variable a to a new variable named b just makes b point to the same object that a does.
  11. 11. Data: Types, Values, Variables, and Names In this code, Python did the following:  Created an integer object with the value 5  Made a variable y point to that 5 object  Incremented the reference count of the object with value 5  Created another integer object with the value 12  Subtracted the value of the object that y points to (5) from the value 12 in the (anonymous) object with that value  Assigned this value (7) to a new (so far, unnamed) integer object  Made the variable x point to this new object  Incremented the reference count of this new object that x points to
  12. 12. Python Numbers This data type supports only numerical values like 1, 31.4, - 1000, 0.000023, 88888888. Python supports 3 different numerical types. 1. int - for integer values like 1, 100, 2255, -999999, 0, 12345678. 2. float - for floating-point values like 2.3, 3.14, 2.71, -11.0. 3. complex - for complex numbers like 3+2j, -2+2.3j, 10j, 4.5+3.14j.
  13. 13. Python operators
  14. 14. Augmented Assignment Operator  These operator allows you write shortcut assignment statements. For e.g:
  15. 15. Bases  You can go the other direction, converting an integer to a string with any of these bases: >>> value = 65 >>> bin(value) '0b1000001' >>> oct(value) '0o101' >>> hex(value) '0x41’  The chr() function converts an integer to its single character string equivalent: >>> chr(65) ‘A’  And ord() goes the other way: >>> ord('A') 65
  16. 16. Number Type Conversion  To change other Python data types to an integer, use the int() function. >>> int(True) 1 >>> int(False) 0  Turning this around, the bool() function returns the boolean equivalent of an integer: >>> bool(1) True >>> bool(0) False >>> int(98.6) 98 >>> int(1.0e4) 10000
  17. 17. Number Type Conversion  To getting the integer value from a text string>>> int(True) >>> int(‘99') 99 >>> int('-23') -23 >>> int('+12') 12 >>> int('1_000_000') 1000000  If the string represents a nondecimal integer, you can include the base: >>> int('10', 2) # binary 2 >>> int('10', 8) # octal 8 >>> int('10', 16) # hexadecimal 16 >>> int('10', 22) # chesterdigital 22
  18. 18. Number Type Conversion  you can convert a string containing characters that would be a valid float >>> float('98.6') 98.6 >>> float('-1.5') -1.5 >>> float('1.0e4') 10000.0  When you mix integers and floats, Python automatically promotes the integer values to float values >>> 43 + 2. 45.0  Python also promotes booleans to integers or floats: >>> False + 0 0 >>> False + 0. 0.0 >>> True + 0 1 >>> True + 0. 1.0
  19. 19. Comment #  You’ll usually see a comment on a line by itself, as shown here: >>> # 60 sec/min * 60 min/hr * 24 hr/day >>> seconds_per_day = 86400  Or, on the same line as the code it’s commenting: >>> seconds_per_day = 86400 # 60 sec/min * 60 min/hr * 24 hr/day
  20. 20. Continue Lines with >>> sum = 1 + ... 2 + ... 3 + ... 4 >>> sum 10 ------------------------------------------------------------------ ---- >>> sum = 1 + File "<stdin>", line 1 sum = 1 + ^ SyntaxError: invalid syntax >>> sum = ( ... 1 + ... 2 + ... 3 + ... 4) >>> >>> sum

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