Python Exam 1

week 1-5: operators, conditional logic, int, float, eval, lists, loops,

program

set of instructions written in a programming language that a computer can execute

programming

the process of creating programs

telling a computer how to solve a problem or

perform an action.

programming includes

• Problem solving (breaking problem into steps)

• Writing instructions in a programming language

• Testing and debugging

assembly languages

First step beyond binary — uses symbols instead of just 0s and 1s

Still low-level: You write instructions that directly control the CPU and memory

High-Level Languages (like Python, Java,

C++)

Easier and more expressive for

humans. They are compiled or interpreted

into machine code

interactive mode

Run Python directly in the shell (>>>prompt)

Each line runs immediately and shows output

Good for quick testing

script mode

Write code in a file (.py) and run it

Runs the whole program at once

Use print() to see results

print()

Displays output to screen

the instruction that tells Python to show something on the screen

immutable

cannot be changed after creation

Any operation that alters the value will create a new object in memory

mutable

can be updated after creation, without creating a new object.

immutable data types

• number

• strings

• tuples

mutable data types

• list

• dictionary

• sets

string

a sequence of characters

Can include letters, digits, or symbols

Written inside 'single', "double", or '''triple''' quotes

numeric data

integers and floats

widely used in calculations

integers

whole numbers no decimals

floats

decimal numbers

Boolean

true or false

tuples

ordered, immutable collections

lists

ordered collection of objects

ordered, changeable collections

dictionaries

key-value pairs

sets

unique items, no order

variables

a name that stores data

Variables point to a value, but we often say the

variable is the value. They can later be changed

to point to something else

variable rules

Must begin with a letter or underscore

Can include letters, digits must begin with a letter or underscore, and underscores

built-in-function name cannot be a variable

assignment statement

gives a variable a value using the ‘=’ sign

input()

lets users type values while program runs

Program pauses until user presses Enter

always returns string

type conversion

int() → number

float() → decimal

str() → text

bool() → True/False

,

automatically spaces values

+

if both sides are numbers, + means add them.

If both sides are strings, + means join them together.

expression

An expression combines values and operators to

produce a result

eval()

expressions with operators/parentheses

takes a string and evaluates it as Python code.

If the string looks like math, it will compute the result.

If the string is a variable name or other valid Python code, it will also try to run it

abs()

absolute value

pow(a, b)

a raised to b

typing rules

Case sensitive

Spaces: indentation matters in Python

Errors appear if spaces are used incorrectly

sep=" "

ensures the words have spaces between them

if statement

used to make decisions in code

checks a Boolean condition (True/False).

If the condition is True, the indented code runs.

If the condition is False, that code is skipped

indentation shows which code belongs to the if

**

exponentiation

//

integer division

gives you the whole number result (rounded down) of a division

%

modulo remainder

Returns the remainder from a division

< >

comparison operator

==

equality operator

!=

not equal to operator

not operator

Reverses the Boolean value of the operand

If the operand is True, it returns False, and vice versa

and operator

Returns True if both operands are True

Otherwise, returns False

or operator

Returns True if at least one operand is True

Returns False only if both operands are False

else statement

executes when the condition is false

elif

When you want to test multiple conditions sequentially in a chained if-else block

type()

returns the type (or class) of the given object useful for inspecting the type of variables or objects at runtime

sys.exit()

ends a Python program immediately

sys.exit(0)

The number 0 means the program exited normally (no error)

Before using sys.exit(), you must import the sys module

random.randint(min, max)

random integer (inclusive range)

must first import random

time.asctime()

returns current time as a string

time.sleep(secs)

pauses the program for secs seconds

random.gauss(mu, sd) 

random float from Gaussian distribution

mu: The mean (average) of the distribution

sigma: The standard deviation (spread) of the distribution

while loop

repeat executing their [indented] code block until the condition becomes false

for loop

repeats something a specific number of times (for loop range (start,stop,step) or range(start,stop))

 A for loop in Python does not include the last stop value from the range

break

stops the loop immediately, even if the condition is still true

continue

skips the rest of the current iteration and continues with the next

list() or []

list function

Create a list with comma-separated values inside square brackets

list index

position number, in square brackets

access an individual element of a list

starts with 0 counting up from the beginning

Or -1 counting down from the end

in

in a condition checks membership (True/False).

in a for loop provides each value as the loop iterates

checks whether a value is in a list (True/False).

Use with if/while for validation.

Use 'not in' to check absence

len()

function to get length of list

list.append(value)

add an item to the end of a list

list.pop(position)

removes item at position

print(list.pop() )

Get and remove the last element

list.sort()

sort a list in place (ascending by default)

list[start:end]

list slicing

slicing

extracts or assigns a range of elements

start is inclusive

end is exclusive indexes separated by a colon

Slices can be open-ended

Slicing can also replace or remove parts, growing or shrinking the list

list[start : end : step]

list slicing using step

start: The index where the slice begins (inclusive). Defaults to 0 if omitted.

stop: The index where the slice ends (exclusive). Defaults to the end of the list if omitted.

step: The interval between elements. Defaults to 1 if omitted.

x.copy()

x[:]

[0:len(x)]

copy

x % 2 == 0

checks if divisible by 2 (even numbers)

range()

generates a sequence of numbers within range, which is commonly used with a for loop to iterate over a specific range of values

inclusive start

exclusive stop

range (start, stop, step)

sum()

adds values within parentheses

min(list)

returns smallest item in a list

max(list)

returns largest item in a list

list[::-1]
list.reverse()

reverse list

list[::2]

even items

+=

adds a value to a variable and then assigns the result back to that variable

[] + []

adds one list to the end of another

[]*value

repeats the list for value

L=[1,2,4,7]

for i in range(len(L)):

print(L[i])

prints out the items of a list, one-by-one, on separate lines

average = sum(list) / len(list)

computes the average of the values in a list

print(list.count(“x”))

returns the number of times x occurs in a list

print(name.index("x"))

returns the location of the first occurrence of x

list.remove(“x“)

removes the first occurrence of x from the list

list.insert(position,”x”)

inserts x at index position on the list

list = [1,2,3,4]

for i in range(len(list)):

list[i] = list[i]**

Replaces each element in a list with its square