Python Basics

Why Python?
 Simple
 Powerful
 Usually preinstalled
 Less Syntax
 Open Source
 Plethora of PenTestTools already created

Interpreted?
• Python is interpreted, which means that python code is translated
and executed by an interpreter one statement at a time.
• This means you can run commands/code on the command
prompt…
• Through a command
prompt with a text file…
• Using an IDE

Good programming proclamations
 Using comments to denote programs or sections of code
◦ A comment beginning with # is called a single-line comment because it
terminates at the end of the current line.
◦ You also may use a multi-line comment—possibly containing many
lines—begins with ’’’ and ends with ’’’.
 You use blank lines, space characters and tab characters (i.e., “tabs”)
to make programs easier to read.
◦ Together, these characters are known as white space.
◦ White-space characters are USUALLY ignored by the interpreter.
◦ Python has its own rules with white space

Printing a Line of Text
• Code: print(“ “) Python 3
• Code: print “ “ Python 2
• Anything placed inside the quotes will be printed on the screen upon execution
of the print command.

Obtaining input
 How to input values from the user
› Code: variable = input(“Prompt “) Python 3
› Code: variable = raw_input(“Prompt”) Python 2
› variable – stores the input from the user.
› input – function to extract user input from the command prompt.
› “Prompt” – a string to inform the user of the type of value to enter.
 Ex. Inputting a numerical value
testGrade1 = input(”Enter test grade 1: “)
testGrade *= 100
print(”Test Grade: “, testGrade, “%”)
Good Programming:Organize outputs, good prompts

DataType Conversion
• Can control how variables are interpreted within the
program:
• Evaluation
• Code: eval(string)
• Ex. eval(“51” + “52”)
• eval( str1 ** str2)
• test = eval(input(“Enter a num”))

Conditional Operators
• Operator Meaning
• == equal to
• < less than
• <= less than or equals to
• > greater than
• >= greater than or equal to
• != not equal to
• Common Mistake:Confusing = with ==

Decision Structures
• Code:
Creating a decision structure:
if (expression):
statement
• To execute more than one statement in a block they must be indented equally:
if (score > 90):
grade = 'A'
print(“Good Job!n”)
print(“Not part of the conditions execution”)
• Good Programming: Commenting conditional blocks
• Common Mistakes: Forgetting equal indent, forgetting :, and forgetting space after if
• Good Practices: Use a tab not a space (harder to line up and troubleshoot)
Space Indent

Nested Conditionals
if (condition):
Statement
elif (condition):
Statement
elif (condition):
Statement
Statement
else:
Statement
• Common Errors: Not Lining up Else with its preceding If.
• Question:Why is a trailing else good programming?

Nested if/else if Example
Question: What zodiac sign is it for the current year?

Logical Operators
Code:
• Using logical operators:
• if (condition or condition)
Statement
• if (condition and condition)
Statement

While Loops
• AWhile Loop is a loop that executes 0 or more times before
terminating.
• Pre-conditional loop
 Code:
 Creating aWhile Loop:
 while (condition statement):
statement1
statement2
 DebuggingTechniques:
 Setup a counter to keep track of the number of times a loop runs
 Set up a counter to count if an event is occurring or the number of
times it occurs
 Output values each time a loop executes

Example
num = eval(input(“Enter a number less than 10:”))
while (num >= 10):
print(“Invalid Entry!”)
num = eval(input(“Enter a number less than 10:”))

For Loops
• For loops are a pre-test loop
• In order to utilize a for loop you need 3 things:
1. Needs to initialize a counter
2. Must test the counter variable (less than)
3. It must update the counter variable
• Code:
for initialization in range(start, stop, increment):
statement1
statement2

Example
for i in range(0, 5, 1):
print(“Hello”)
Step 1: Perform the initialization
expression
Step 2: Evaluate the test expressions
Step 3: Execute the body of the
loop
Step 4: Perform the
update
Assign 0 to i
i < 5
Update iPrint “Hello”
True
False

Function Definition
• Definition includes:
• return value: the value the function returns to the part of the
program that called it
• name: name of the function. Function names follow same rules
as variables
• parameter list: variables containing
values passed to the function
• body: statements that perform
the function’s task

Calling a Function
• Functions just like variables need to be called in order
to be invoked
• Code:
Calling a Function:
 functionName (Parameters)

Write and Calling Functions Example

Modules
• Some special functions have not been innately included into the interpreter to
speed up the loading process, these packages are known as modules.
• Code: import moduleName
• Ex.
• import math
• import random
• Import os
• OS module
• os.getcwd()
• os.chdir(path)

Python Basics

More Related Content

What's hot (20)

Viewers also liked (20)

Similar to Python Basics (20)

More from primeteacher32 (20)

Recently uploaded (20)

Python Basics

Editor's Notes