This document discusses variables, data types, expressions, and functions in Python. It defines a variable as a name that represents a stored value in memory. It describes different data types in Python including integers, floats, strings, Booleans, and others. It also discusses expressions, which represent computations that evaluate to a value, and different expression types like arithmetic, relational, logical, and compound expressions. Finally, it introduces functions as blocks of code that perform tasks and can return values.

1. Topic #2
Input, Output, Expression

3.  A variable is a name that represents a value
stored in the computer memory.
 Location in memory where value can be
stored
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4.  A variable name is any valid identifier that is not a
Python keyword.
 A variable name can not contain spaces.
 A first character must be characters or an
underscore ( _ ).
 Cannot begin with digit
 After first character, the digits 0 through 9 can be
used.
 Case sensitive. Uppercase and lower case are
distinct. This means the variable name ItemOrdered
is not the same as itemordered.
 Choosing meaningful identifiers helps make a
program self-documenting.
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5. Variable Name Legal or Illegal
Units_per_day Legal
dayOfWeek Legal
3dGraphic Illegal. Variable name cannot
begins with digit
June1997 Legal
Mixture#3 Illegal. Variable name may only use
letters, digits, or underscore
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6.  The variable name begins with lowercase
letters.
 The first character of the second and
subsequent words is written in Uppercase
◦ grossPay
◦ payRate
◦ averageOfNumbers
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7. Assignment operator =
 Assigns value on right to variable on left.
Number1 = 45
Number2 = 72
Sum = Number1 + Number2
>>> print(Number1)
45
>>> print(Number2)
72
>>> print(Sum)
117
Note: Variable can not be used until it is assigned a value
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9.  There are some words that are reserved by
Python for its own use. You can't name variable
with the same name as a keyword. To get a list of
all the keywords, issue the following command
>>> import keyword
>>> keyword.kwlist
['False', 'None', 'True', 'and', 'as', 'assert', 'break',
'class', 'continue', 'def', 'del', 'elif', 'else', 'except',
'finally', 'for', 'from', 'global', 'if', 'import', 'in', 'is',
'lambda', 'nonlocal', 'not', 'or', 'pass', 'raise', 'return',
'try', 'while', 'with', 'yield']
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10.  If you give the statement to python to
evaluate,
>>> x=6
It will associate the value of the expression on
the right hand side with the name x.
An assignment statement has the following
form:
variable_name = expression
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11.  Python evaluates an assignment statement
using the following rules
◦ Evaluate the expression on the right hand side of
the statement. This will result in a value.
◦ Store the id in the variable.
 You can now reuse the variable
>>> x=9
>>>x*8
72
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12.  As the name indicates, Python variables can be
readily changed. This means that you can
connect a different value with a previously
assigned variable very easily through simple
reassignment.
 Knowing that you can readily and easily reassign
a variable can also be useful in situations where
you may be working on a large program that was
begun by someone else and you are not clear yet
on what has already been defined.
 See related shell examples
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13.  With Python, you can assign one single value
to several variables at the same time.
 This lets you initialize several variables at
once, which you can reassign later in the
program yourself, or through user input.
>>> x = y = z = 0
>>> j , k , l = ‘shark’ , 2.5 , 5
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15.  Computers manipulate data values that represent
information and these values can be of different types.
 In fact, each value in a Python program is of a specific
type.
 The data type of a value determines how the data is
represented in the computer and what operations can be
performed on that data.
 A data type provided by the language itself is called a
primitive data type.
 Python supports quite a few data types: numbers, text
strings, files, containers, and many others.
 Programmers can also define their own user-defined
data types, which we will cover in detail later.
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16. 16

17.  Expressions are representation in text of
some form of computation.
 Expressions are distinguished by the fact that
when you evaluate (perform the represented
computation) you end up with a resultant
value.
>>> 5
5
>>> 5+6
11
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18.  An expression that represents the resultant
internal value that it generates inside the
interpreter. 10 is a primitive expression 10 +
10 is not.
 Numerical Data Types -- int, float, complex
◦ See Shell for examples
 Strings
◦ "your name“
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20.  Arithmetic
◦ +, -, *, /, //, %, **
 Relational
◦ >, >, >=, <=, ==, !=
 Logical
and, or, not
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22.  The precedents of math operators from
highest to lowest is
◦ Exponentiation **
◦ Multiplication, Division, Remainder *, /, //, %,
◦ Addition and subtraction +, -
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23. Expression Value
5 + 2 * 4
10 / 2 - 3
8 + 12 * 2 - 4
6 - 3 * 2 + 7 - 1
(6 - 3) * 2 + 7 - 1
10 / (5 - 3) * 2
(6 - 3) * (2 + 7) / 3
8 + 12 * (6 - 4)
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25. 25

26.  first include the statement
 from math import sqrt
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28. 28

29. Expression Value of the Expression
True and False False
False and True False
False and False False
True and True True
Expression Value of the Expression
True or False True
False or True True
False or False False
True or True True
Expression Value of the Expression
not True False
Not False True
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30.  A Boolean expression is an expression that
evaluates to True or False
>>> 4 > 2
True
>>> 4 < 2
False
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31.  True and False are not strings, they are
special values that belong to the type bool
>>> type(True)
<class 'bool'>
>>> type(4 < 2)
<class 'bool'>
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32.  How do you explain this?
>>> False or 1
1
>>> True and 0
0
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33.  To understand this behavior you need to
learn the following rule:
“The integer 0, the float 0.0, the empty string,
the None object, and other empty data
structures are considered False; everything else
is interpreted as True"
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34.  When an expression contains And or Or,
Python evaluates from left to right
 It stops evaluating once the truth value of the
expression is known
◦ For x and y, if x is False, there is no reason to
evaluate y
◦ For x or y, if x is True, there is no reason to
evaluate y
 The value of the expression ends up being
the last condition actually evaluated by
Python
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35. Try to evaluate the value of the following
expressions
◦ 0 and 3
◦ 3 and 0
◦ 3 and 5
◦ 1 or 0
◦ 0 or 1
◦ True or 1 / 0
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36. In the following expression, which parts are
evaluated?
◦ (7 > 2) or ( (9 < 2) and (8 > 3) )
◦ A. Only the first condition
◦ B. Only the second condition
◦ C. Only the third condition
◦ D. The first and third conditions
◦ E. All of the code is evaluated
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37.  What is the output of the following code?
a = 3
b = (a != 3)
print(b)
A. True
B. False
C. 3
D. Syntax error
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38.  Consider the following expression:
(not a) or b
 Which of the following assignments makes
the expression False?
A. a = False; b = False
B. a = False; b = True
C. a = True; b = False
D. a = True; b = True
E. More than one of the above
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39.  Consider the following expression:
a and (not b)
Which of the following assignments makes the
expression False?
A. a = False; b = False
B. a = False; b = True
C. a = True; b = False
D. a = True; b = True
E. More than one of the above
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40.  What happens when we evaluate the
following?
>>> 1 or 1/0 and 1
When expressions involve Boolean and & or
operators, short circuiting is applied first and
then precedence is used.
What is the value of the following expression?
>>>1 or 1/0
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42.  function is a collection of programming
instructions that carry out a particular task.
 For Example: Print function to display
information.
 There are many other functions available in
Python.
 Most functions return a value. That is, when the
function completes its task, it passes a value
back to the point where the function was called.
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43. Function call expression
Function call expressions are of the form
function_name(arguments)
See Shell for examples
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44.  Print function is a piece of prewritten code that
performs an operation. Python has numerous
built-in functions that perform various
operations.
Print(“Hello World”)
In interactive mode, type this statement and press
the Enter key, the message Hello world is
displayed.
Here is an example:
>>> print('Hello world')
Hello world
>>>
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45.  Python also allows you to enclose string literals in triple
quotes (either """ or ' '). Triple-quoted strings can
contain both single quotes and double quotes as part of
the string.
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46. >>> print("""One
Two
Three""")
One
Two
Three
>>> print("""One Two Three""")
One Two Three
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47.  Comments are notes of explanation that
document lines or sections of a program.
Comments are part of the program, but the
Python interpreter ignores them. They are
intended for people who may be reading the
source code.
 In Python, comment begin with the # character.
When the Python interpreter sees a # character, it
ignores everything from that character to the end
of the line.
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49.  Python built-in functions to read input from
the keyboard.
Variable = input(prompt)
x= input("Enter First Number : ")
name = input(“Whats is your Name : ")
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50. >>> name = input(“ What is your Name : ")
What is your Name : Ahmed
>>> print(name)
Ahmed
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51.  Input function always returns user input as a
string, even if the user enter numeric data.
 Use data conversion function.
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53. >>> x= float(input("Enter First Number : "))
Enter First Number : 10
>>> y= float(input("Enter second Number : "))
Enter second Number : 3
>>> z= float(input("Enter Third Number : "))
Enter Third Number : 5
>>> print("The maximum value is : ", max(x,y,z))
The maximum value is : 10.0
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54.  An expression that is formed by combining
multiple expressions together.
 For example 4 + len("abc") is a compound
expression formed from a primitive
expressions ('4') and a function call
expression (len("abc")) using the addition
operator.
 See shell for related examples
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55.  Go over sections 2.1, 2.2 and 2.5 of the
Textbook.
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