Python Cheatsheet

1. Common Data Types
int, float – numbers
str – text
list – ordered, changeable collection
dict – key-value pairs
tuple – like list, but unchangeable
set – unique, unordered items

2. Essential Functions
print() – display output
type() – check data type
len() – count items
range() – generate numbers
input() – take user input

3. String Methods
.upper(), .lower() – change case
.strip() – remove whitespace
.replace() – swap text
.split() – break into list

4. List Methods
append() – add item
pop() – remove item
sort() – sort list
[1:4] – slicing (get part of list)

5. Dictionary Basics
Access: mydict['key']
Safe access: mydict.get('key')
Add/Update: mydict['new'] = value

6. Control Flow
if / elif / else – conditions
for – loop over items
while – loop with condition
break / continue – control loop

7. Functions
def – define a function
return – return a value
lambda – short anonymous function

8. Useful Built-in Modules
math – sqrt, pi, round
random – random numbers, choices
datetime – current date/time
os – system & file handling

9. Popular Libraries for Data Work
NumPy – numerical operations
Pandas – dataframes and analysis
Matplotlib

*Variables & Data Types in Python*

What are Variables?
Variables are used to store data so you can refer to it and manipulate it later in your code. You don’t need to declare the type of variable explicitly in Python — it figures it out based on the value you assign.

Example:
x = 10 name = Alice price = 19.99 is_active = True

Data Types in Python

int – Integer numbers
Example: x = 5

float – Decimal numbers
Example: pi = 3.14

str – String or text
Example: name = John

bool – Boolean values (True or False)
Example: is_logged_in = False

list – An ordered, changeable collection
Example: fruits = [apple, banana, cherry]

tuple – An ordered, unchangeable collection
Example: coordinates = (10, 20)

set – An unordered collection of unique items
Example: unique_ids = 1, 2, 3

dict – A collection of key-value pairs
Example: person = name: Alice, age: 25

*Control Flow (if, elif, else) in Python*

What is Control Flow?

Control flow allows your code to make decisions. You use if, elif, and else statements to run different blocks of code depending on conditions.

Basic Structure:

if condition:
code runs if condition is True
elif another_condition:
code runs if the second condition is True
else:
code runs if none of the above are True

Example:

age = 20

if age 18:
print(You are a minor.)
elif age == 18:
print(You just became an adult!)
else:
print(You are an adult.)

Comparison Operators:

== (equal to)

!= (not equal to)

(less than)

= (less than or equal to)

= (greater than or equal to)


Logical Operators:

and – Both conditions must be True

or – At least one condition must be True

not – Reverses the result (True becomes False)


Example with logical operators:

age = 25
is_student = False

if age 18 and not is_student:
print(Eligible for the job.)

*_Let's go through important Python Topics Everyday starting with the first one today_*

*Variables & Data Types in Python*

What are Variables?
Variables are used to store data so you can refer to it and manipulate it later in your code. You don’t need to declare the type of variable explicitly in Python — it figures it out based on the value you assign.

Example:
x = 10 name = Alice price = 19.99 is_active = True

Data Types in Python

int – Integer numbers
Example: x = 5

float – Decimal numbers
Example: pi = 3.14

str – String or text
Example: name = John

bool – Boolean values (True or False)
Example: is_logged_in = False

list – An ordered, changeable collection
Example: fruits = [apple, banana, cherry]

tuple – An ordered, unchangeable collection
Example: coordinates = (10, 20)

set – An unordered collection of unique items
Example: unique_ids = 1, 2, 3

dict – A collection of key-value pairs
Example: person = name: Alice, age: 25

*Control Flow (if, elif, else) in Python*

What is Control Flow?

Control flow allows your code to make decisions. You use if, elif, and else statements to run different blocks of code depending on conditions.

Basic Structure:

if condition:
code runs if condition is True
elif another_condition:
code runs if the second condition is True
else:
code runs if none of the above are True

Example:

age = 20

if age 18:
print(You are a minor.)
elif age == 18:
print(You just became an adult!)
else:
print(You are an adult.)

Comparison Operators:

== (equal to)

!= (not equal to)

(less than)

= (less than or equal to)

= (greater than or equal to)


Logical Operators:

and – Both conditions must be True

or – At least one condition must be True

not – Reverses the result (True becomes False)


Example with logical operators:

age = 25
is_student = False

if age 18 and not is_student:
print(Eligible for the job.)

*Loops in Python (for & while)*

What are Loops?

Loops let you repeat a block of code multiple times. They’re essential for tasks like iterating over data, automating repetitive steps, or checking conditions.


1. For Loop

Used to iterate over a sequence like a list, string, or range.

Example:

fruits = [apple, banana, cherry]

for fruit in fruits:
print(fruit)

You can also use range() to loop a specific number of times:

for i in range(5):
print(i)


2. While Loop

Repeats as long as a condition is True.

Example:

count = 0

while count 3:
print(Count is:, count)
count += 1


Loop Control Statements:

break – exits the loop completely

continue – skips the current iteration and continues with the next

pass – does nothing (used as a placeholder)


Example:

for i in range(5):
if i == 3:
break
print(i)

*Dictionaries in Python*

A dictionary is a collection of key-value pairs. Each key is unique and maps to a value. Dictionaries are unordered (until Python 3.7) and mutable, meaning you can change them.


*Creating a Dictionary:*

person =
name: Alice,
age: 25,
city: New York



*Accessing Values* :

print(person[name]) Output: Alice
print(person.get(age)) Output: 25

Using .get() is safer because it won’t crash if the key doesn’t exist.

*Adding or Updating Items:*

person[email] = alice@example.com Add new key
person[age] = 26 Update value


*Deleting Items:*

del person[city]


*Looping through a Dictionary:*

for key, value in person.items():
print(key, :, value)


*Why Use Dictionaries?*

- Fast access via keys

- Ideal for storing structured data (like a JSON object)

- Very flexible in combining with loops and functions

*Powerful One-Liners in Python You Should Know!*


1. *Swap Two Numbers*

n1, n2 = n2, n1


2. *Reverse a String*

reversed_string = input_string[::-1]


3. *Factorial of a Number*

fact = lambda n: [1, 0][n 1] or fact(n - 1) * n


4. *Find Prime Numbers (2 to 10)*

primes = list(filter(lambda x: all(x % y != 0 for y in range(2, x)), range(2, 10)))


5. *Check if a String is Palindrome*

palindrome = input_string == input_string[::-1]