Online Help for Python Programming Homework
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What is Scripting Language? 
A scripting language is a “wrapper” language that integrates OS 
functions. 
• The interpreter is a layer of software logic between your code 
and the computer hardware on your machine. Wiki Says: 
• The “program” has an executable form that the computer can 
use directly to execute the instructions. 
• The same program in its human-readable source code form, 
from which executable programs are derived (e.g., compiled) • 
Python is scripting language, fast and dynamic. 
• Python is called ‘scripting language’ because of it’s scalable 
interpreter, but actually it is much more than that
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                       What is Python? 
Python is a high-level programming language which is: 
 Interpreted: Python is processed at runtime by the interpreter. 
(Next Slide) 
 Interactive: You can use a Python prompt and interact with the 
interpreter directly to write your programs. 
 Object-Oriented: Python supports Object-Oriented technique of 
programming. 
 Beginner’s Language: Python is a great language for the 
beginner-level programmers and supports the development of a 
wide range of applications. 8/22/201
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Languages
 Some influential ones:
 FORTRAN
 science / engineering
 COBOL
 business data
 LISP
 logic and AI
 BASIC
 a simple language
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Programming basics
 code or source code: The sequence of instructions in a program.
 syntax: The set of legal structures and commands that can be 
used in a particular programming language.
 output: The messages printed to the user by a program.
 console: The text box onto which output is printed.
 Some source code editors pop up the console as an external window, 
and others contain their own console window.
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Compiling and interpreting
 Many languages require you to compile (translate) your program 
into a form that the machine understands.
compile execute
source code byte code output
Hello.java Hello.class
 Python is instead directly interpreted into machine instructions.
interpret
source code output
Hello.py
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Expressions
 expression: A data value or set of operations to compute a value.
Examples: 1 + 4 * 3
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 Arithmetic operators we will use:
 + - * / addition, subtraction/negation, multiplication, division
 % modulus, a.k.a. remainder
 **  exponentiation
 precedence: Order in which operations are computed.
 * / % ** have a higher precedence than + -
1 + 3 * 4 is 13
 Parentheses can be used to force a certain order of evaluation.
(1 + 3) * 4 is 16
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Integer division
 When we divide integers with / , the quotient is also an integer.
        3                      52
   4 ) 14               27 ) 1425
       12                    135
        2                      75
                               54
                               21
 More examples:
 35 / 5  is  7
 84 / 10  is  8
 156 / 100  is  1
 The % operator computes the remainder from a division of integers.
        3                        43
   4 ) 14                   5 ) 218
       12                       20
        2                        18
                                 15
                                  3
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Real numbers
 Python can also manipulate real numbers.
 Examples: 6.022 -15.9997 42.0 2.143e17
 The operators + - * / % **  ( ) all work for real numbers.
 The / produces an exact answer: 15.0 / 2.0 is 7.5
 The same rules of precedence also apply to real numbers:
Evaluate  ( )  before  * / %  before  + -
 When integers and reals are mixed, the result is a real number.
 Example:  1 / 2.0  is  0.5
 The conversion occurs on a per-operator basis.
 7 / 3 * 1.2 + 3 / 2
   2   * 1.2 + 3 / 2
     2.4     + 3 / 2
     2.4     +   1
          3.4
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print
 print : Produces text output on the console.
 Syntax:
print "Message"
print Expression
 Prints the given text message or expression value on the console, and 
moves the cursor down to the next line.
print Item1, Item2, ..., ItemN
 Prints several messages and/or expressions on the same line.
 Examples:
print "Hello, world!"
age = 45
print "You have", 65 - age, "years until retirement"
Output:
Hello, world!
You have 20 years until retirement
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input
 input : Reads a number from user input.
 You can assign (store) the result of input into a variable.
 Example:
age = input("How old are you? ")
print "Your age is", age
print "You have", 65 - age, "years until retirement"
Output:
How old are you? 53
Your age is 53
You have 12 years until retirement
 Exercise: Write a Python program that prompts the user for 
his/her amount of money, then reports how many Nintendo Wiis 
the person can afford, and how much more money he/she will need 
to afford an additional Wii.
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The for loop
 for loop: Repeats a set of statements over a group of values.
 Syntax:
for variableName in groupOfValues:
    statements
 We indent the statements to be repeated with tabs or spaces.
 variableName gives a name to each value, so you can refer to it in the statements.
 groupOfValues can be a range of integers, specified with the range function.
 Example:
for x in range(1, 6):
    print x, "squared is", x * x
Output:
1 squared is 1
2 squared is 4
3 squared is 9
4 squared is 16
5 squared is 25
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Cumulative loops
 Some loops incrementally compute a value that is initialized outside 
the loop.  This is sometimes called a cumulative sum.
sum = 0
for i in range(1, 11):
    sum = sum + (i * i)
print "sum of first 10 squares is", sum
Output:
sum of first 10 squares is 385
 Exercise: Write a Python program that computes the factorial of 
an integer.
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if
 if statement: Executes a group of statements only if a certain 
condition is true.  Otherwise, the statements are skipped.
 Syntax:
if condition:
    statements
 Example:
gpa = 3.4
if gpa > 2.0:
    print "Your application is accepted."
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if/else
 if/else statement: Executes one block of statements if a certain 
condition is True, and a second block of statements if it is False.
 Syntax:
if condition:
    statements
else:
    statements
 Example:
gpa = 1.4
if gpa > 2.0:
    print "Welcome to Mars University!"
else:
    print "Your application is denied."
 Multiple conditions can be chained with elif ("else if"):
if condition:
    statements
elif condition:
    statements
else:
    statements
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while
 while loop: Executes a group of statements as long as a condition is True.
 good for indefinite loops (repeat an unknown number of times)
 Syntax:
while condition:
    statements
 Example:
number = 1
while number < 200:
    print number, 
    number = number * 2
 Output:
1 2 4 8 16 32 64 128
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File processing
 Many programs handle data, which often comes from files.
 Reading the entire contents of a file:
variableName = open("filename").read()
Example:
file_text = open("bankaccount.txt").read()
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