Scripting Exam

Compiler

A compiler translates the whole source program into another form, often machine code or bytecode, before the program runs. After compilation, the resulting program can usually run faster because the translation is already done.

Interpreter

An interpreter executes code step by step. Python is commonly described as interpreted because code can be run interactively and executed line by line by the python runtime.

Translation

• Compiler: Usually translates the entire program before execution

• Interpreter: Executes statements as the program runs

Error Discovery

• Compiler: May report many syntax errors before running

• Interpreter: May stop when it reaches the error

Speed

• Compiler: Often faster after compilation

• Interpreter: often slower because execution includes interpretation

Python Identifier Rules

• Can contain letters, digits, and underscores

• cannot start with a digit (number)

• cannot contain spaces or symbols like @, %, -, or $

• cannot be a python keyword such as if, else, for, import, class, or while

• identifiers are case-sensitive: name, Name, and NAME are different

Comments

a comment is ignored by Python and is used to explain code

Single, double, and triple quotes

Single quotes and double quotes both create strings. Triple quotes are useful for multi-line strings

Escape Sequences

An escape sequence begins with a backlash. The exam review specifically mentions the difference between n and \n

n

• Meaning: just the letter n

• Example output: HellonWorld

\n

• Meaning: Newline character

• Example output: Hello then World on the next line

\t

• Meaning: Tab character

• Ex: Adds spacing like a tab

\\

• Meaning: Literal backslash

• Ex: Prints one backslash

+

addition (10+3=13)

-

Subtraction

*

Multiplication

/

Regular division (10/3=3.333)

//

Floor division 10//3=3

%

Modulus/Remainder (10%3=1)

**

Exponent (2**3=8)

==

Equal to

!=

Not equal to

>

greater than

<

Less than

>=

Greater than or equal to

<=

Less than or equal to

and

• Meaning: Both conditions must be true

• Ex: age > 18 and age < 30

or

• Meaning: At least one condition must be true

• Ex: x == 1 or x == 2

not

• Meaning: reverses the Boolean value

• Ex: not True is False

string

• Key idea: text, indexed and sliceable

• Ex: “hello”

integer

• Key idea: Whole number

• Ex: 20

float

• Key idea: Decimal

• Ex: 19.99

Boolean

• Key idea: represent truth values

• Ex: True/False

list

• Key idea: Ordered and Mutable

• Ex: [1,2,3]

tuple

• Key idea: Ordered and immutable

• Example: (1,2,3)

dictionary

• Key idea: key value pairs

• Ex: {“name”: “Chris”}

set

• Key idea: Unordered, no duplicates; can contain different data types

• Ex: {1,2,3}

List vs. Tuple

A list can be changed after it is created. A tuple cannot be changed after its created

Indexing

Python Indexing starts at 0. Negative indexing starts from the end

Slicing

Slice format is [start:stop:step]. The start index is included, but the stop index is not included.

Dictionary

A dictionary stores data as key value pairs. You use the key to access the value

keys()

• returns all keys

• ex: student.keys()

values()

• returns all values

• Ex: student.values()

items()

• returns key value pairs

• Ex: student.items()

update()

• Updates or adds data

• Ex: student.update({"age": 21})

pop()

• Removes a key and returns its value

• student.pop(“age”)

setdefault()

• Gets value if key exists; otherwise inserts default

• Ex: student.setdefault(“school”. “UMB”)

if, elif, and else

Conditional statements allow a program to make decisions. Python checks the conditions from top to bottom and stops after the first true condition.

Order Matters

if a condition is true, then python skips the remaining elif and else blocks

os

Work with directories, paths, and the operating systems

sys

interact with the Python runtime; common example is sys.exit()

Import and Modules

the import keyword loads code from another module so you can use its functions, constants, or classes

pprint

pretty-print complex structures like dictionaries

shutil

Higher-level file operations such as copying files

random

Generate random numbers

for Loops

A for loop repeats code for each item in a sequence, such as a list, string, or range

range()

generates an immutable sequence of numbers

range(5)

• 0 through stop

• values produed: 0,1,2,3,4

range(1, 5)

• start through stop

• 1,2,3,4

range(1, 10, 2)

• start, stop, step

• 1,3,5,7,9

break

stops the loop completely

continue

skips the rest of the current iteration and moves to the next one

Strings

immutable sequences of characters

len(s)

• returns length

• len(“abc”) is 3

s.upper()

• Uppercase copy

• Original string is not changed unless reassigned

s.lower()

• Lowercase copy

• useful for case-insensitive checks

s.find()

• first index of x

• returns -1 if not found

s.rfind()

• last index of x

• searches from the right

s.index(x)

• first index of x

• raises ValueError if not found

s.startswith(x)

• checks beginning

• returns true or false

s.endswith(x)

• checks ending

• returns True or False

s.split(sep)

• Splits string into list

• Default split separates on whitespace

sep.join(list)

• Joins list into string

• the separator goes between items

Random Module

The random module generates pseudo-random values

random.random()

• Returns: Float from 0.0 up to but not including 1.0.

• Ex: 0.72834

random.uniform(a, b)

• Returns: Float between a and b

• random.uniform(1,10)

random.randint(a,b)

• returns: integer from a through b, including both endpoints

• Ex: random.randint(1, 10) can return 1 or 10.

OS Module

is central for cybersecurity scripting because scripts often need to inspect folders, check file types, build paths, and collect evidence files

os.chdir(path)

Changes the current working directory.

os.getcwd()

Returns the current working directory

os.listdir(path)

Lists files and folders inside a directory

os.path.getsize(path)

Returns size in bytes.

os.path.isfile(path)

True if path is a file

os.path.isdir(path)

True if path is a directory.

os.path.exists(path)

True if path exists.

os.path.basename(path)

Returns final file/folder name from a path

os.path.dirname(path)

Returns the directory portion of a path.

os.path.relpath(path)

Returns a relative path.

os.path.abspath(path)

Returns an absolute/full path.

os.path.join(a, b, ...)

Safely combines path parts.

os.mkdir(path)

Creates one directory level.

os.makedirs(path)

Creates nested directories.

Windows File Path Separator

• Backslash \

• C:\Users\Chris\Desktop\file.txt

Linux/macOS File Path Separator

• Forward slash /

• /home/chris/Desktop/file.txt

File pointer

is the current position inside a file. Reading and writing start from the pointer position

r (read)

• pointer position: Beginning

• reads an existing file

w (write)

• pointer position: beginning after file is erased

• overwrites existing file or creates a new file

a (append)

• pointer position: end

• appends new data to the end

Binary File Modes

are used for non text files such as images, PDFs, executables, disk images, and other forensic evidence files

rb (read binary)

• open image/evidence file for reading