This skill is ideal for complete beginners learning Python from scratch, or anyone who wants a quick refresher on Python fundamentals for writing simple scripts and automation.

Python Basics

A comprehensive guide to Python fundamentals — variables, data types, control flow, functions, and core data structures. Everything you need to start writing Python scripts and building small programs.

When to Use This Skill

Learning Python as your first programming language
Writing simple automation scripts
Understanding variables, types, and basic operations
Working with lists, dictionaries, and other collections
Building small command-line tools
Preparing for more advanced Python topics

Variables and Data Types

Declaring Variables

Python uses dynamic typing — no need to declare types explicitly.

PYTHON

# Strings
name = "Alice"
greeting = 'Hello, World!'
multiline = """This spans
multiple lines"""

# Numbers
age = 30            # int
price = 19.99       # float
big_number = 1_000_000  # underscores for readability

# Booleans
is_active = True
is_deleted = False

# None (null equivalent)
result = None

Type Checking and Conversion

PYTHON

# Check types
type(42)        # <class 'int'>
type("hello")   # <class 'str'>
isinstance(42, int)  # True

# Convert between types
int("42")       # 42
str(42)         # "42"
float("3.14")   # 3.14
bool(0)         # False
bool(1)         # True
list("abc")     # ['a', 'b', 'c']

String Operations

PYTHON

name = "Alice"

# f-strings (Python 3.6+)
print(f"Hello, {name}!")        # Hello, Alice!
print(f"Length: {len(name)}")   # Length: 5

# Common methods
"hello world".upper()           # "HELLO WORLD"
"HELLO".lower()                 # "hello"
"  spaced  ".strip()            # "spaced"
"hello world".split()           # ["hello", "world"]
", ".join(["a", "b", "c"])      # "a, b, c"
"hello".replace("l", "r")       # "herro"
"hello world".startswith("hello")  # True

# Slicing
text = "Python"
text[0]      # "P"
text[-1]     # "n"
text[0:3]    # "Pyt"
text[::2]    # "Pto"
text[::-1]   # "nohtyP" (reversed)

Operators

Common Operators

Arithmetic: +, -, *, /, // (floor div), % (modulo), ** (power)
Comparison: ==, !=, <, >, <=, >=
Logical: and, or, not
Membership: in, not in
Identity: is, is not

PYTHON

# Arithmetic
10 / 3      # 3.333...
10 // 3     # 3 (floor division)
10 % 3      # 1 (remainder)
2 ** 10     # 1024 (power)

# Membership
"a" in "abc"          # True
3 in [1, 2, 3]        # True
"key" in {"key": 1}   # True

# Identity (checks same object, not equality)
a = [1, 2]
b = [1, 2]
a == b    # True (same value)
a is b    # False (different objects)

Control Flow

Conditionals

PYTHON

age = 18

if age < 13:
    print("Child")
elif age < 18:
    print("Teenager")
else:
    print("Adult")

# Ternary expression
status = "adult" if age >= 18 else "minor"

# Match statement (Python 3.10+)
match command:
    case "start":
        begin()
    case "stop":
        end()
    case _:
        print("Unknown command")

For Loops

PYTHON

# Iterate over a list
fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

# Range-based loops
for i in range(5):          # 0, 1, 2, 3, 4
    print(i)

for i in range(2, 8):       # 2, 3, 4, 5, 6, 7
    print(i)

for i in range(0, 10, 2):   # 0, 2, 4, 6, 8
    print(i)

# Enumerate (get index + value)
for i, fruit in enumerate(fruits):
    print(f"{i}: {fruit}")

# Iterate over dictionary
scores = {"Alice": 95, "Bob": 87}
for name, score in scores.items():
    print(f"{name}: {score}")

While Loops

PYTHON

count = 0
while count < 5:
    print(count)
    count += 1

# Break and continue
for i in range(10):
    if i == 3:
        continue   # skip 3
    if i == 7:
        break      # stop at 7
    print(i)       # prints 0, 1, 2, 4, 5, 6

Functions

Defining Functions

PYTHON

def greet(name):
    """Return a greeting message."""
    return f"Hello, {name}!"

print(greet("Alice"))  # Hello, Alice!

# Default parameters
def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

greet("Alice")            # Hello, Alice!
greet("Alice", "Hey")     # Hey, Alice!

# Multiple return values
def divide(a, b):
    quotient = a // b
    remainder = a % b
    return quotient, remainder

q, r = divide(17, 5)  # q=3, r=2

Args and Kwargs

PYTHON

# *args — variable positional arguments
def total(*numbers):
    return sum(numbers)

total(1, 2, 3)      # 6
total(10, 20)        # 30

# **kwargs — variable keyword arguments
def build_profile(**info):
    return info

build_profile(name="Alice", age=30)
# {'name': 'Alice', 'age': 30}

Lambda Functions

PYTHON

# Short anonymous functions
double = lambda x: x * 2
double(5)  # 10

# Common with built-in functions
numbers = [3, 1, 4, 1, 5]
sorted(numbers, key=lambda x: -x)  # [5, 4, 3, 1, 1]

names = ["alice", "Bob", "CHARLIE"]
sorted(names, key=lambda s: s.lower())  # ['alice', 'Bob', 'CHARLIE']

Data Structures

Lists

PYTHON

# Create
fruits = ["apple", "banana", "cherry"]
numbers = list(range(1, 6))  # [1, 2, 3, 4, 5]

# Access and modify
fruits[0]           # "apple"
fruits[-1]          # "cherry"
fruits[1] = "blueberry"

# Add items
fruits.append("date")         # add to end
fruits.insert(1, "avocado")   # insert at index
fruits.extend(["fig", "grape"])  # add multiple

# Remove items
fruits.remove("banana")   # remove by value
fruits.pop()               # remove last item
fruits.pop(0)              # remove by index
del fruits[0]              # delete by index

# List comprehensions
squares = [x**2 for x in range(10)]
evens = [x for x in range(20) if x % 2 == 0]
pairs = [(x, y) for x in range(3) for y in range(3)]

# Useful operations
len(fruits)          # length
sorted(fruits)       # sorted copy
fruits.sort()        # sort in place
fruits.reverse()     # reverse in place
"apple" in fruits    # membership check

Dictionaries

PYTHON

# Create
person = {"name": "Alice", "age": 30, "city": "NYC"}
also_valid = dict(name="Alice", age=30)

# Access
person["name"]              # "Alice"
person.get("email", "N/A")  # "N/A" (default if key missing)

# Modify
person["age"] = 31                  # update
person["email"] = "alice@mail.com"  # add new key
del person["city"]                  # remove

# Iterate
for key in person:
    print(key)

for key, value in person.items():
    print(f"{key}: {value}")

# Dictionary comprehension
squares = {x: x**2 for x in range(6)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

# Useful methods
person.keys()     # dict_keys(['name', 'age', 'email'])
person.values()   # dict_values(['Alice', 31, 'alice@mail.com'])
person.items()    # key-value pairs
person.update({"age": 32, "role": "dev"})  # merge

Tuples and Sets

PYTHON

# Tuples — immutable, ordered
point = (3, 4)
x, y = point        # unpacking
single = (42,)       # single-element tuple needs trailing comma

# Sets — unique, unordered
colors = {"red", "green", "blue"}
colors.add("yellow")
colors.discard("red")

# Set operations
a = {1, 2, 3, 4}
b = {3, 4, 5, 6}
a | b    # union: {1, 2, 3, 4, 5, 6}
a & b    # intersection: {3, 4}
a - b    # difference: {1, 2}
a ^ b    # symmetric difference: {1, 2, 5, 6}

File I/O

PYTHON

# Read a file
with open("data.txt", "r") as f:
    content = f.read()           # entire file as string
    # or
    lines = f.readlines()       # list of lines

# Write a file
with open("output.txt", "w") as f:
    f.write("Hello, World!\n")

# Append to a file
with open("log.txt", "a") as f:
    f.write("New log entry\n")

# Read line by line (memory-efficient for large files)
with open("data.txt") as f:
    for line in f:
        print(line.strip())

Always use the with statement when working with files. It automatically closes the file when the block ends, even if an error occurs.

Error Handling

PYTHON

# Basic try/except
try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero!")

# Multiple exceptions
try:
    value = int(input("Enter a number: "))
    result = 100 / value
except ValueError:
    print("That's not a valid number!")
except ZeroDivisionError:
    print("Cannot divide by zero!")
except Exception as e:
    print(f"Unexpected error: {e}")
finally:
    print("This always runs")

# Raise exceptions
def validate_age(age):
    if age < 0:
        raise ValueError("Age cannot be negative")
    return age

Modules and Imports

PYTHON

# Import entire module
import os
import json

# Import specific items
from pathlib import Path
from datetime import datetime, timedelta

# Import with alias
import numpy as np

# Common standard library modules
import os           # file paths, environment variables
import sys          # system-specific parameters
import json         # JSON encoding/decoding
import csv          # CSV file reading/writing
import math         # mathematical functions
import random       # random number generation
import datetime     # date and time handling
import pathlib      # object-oriented file paths
import re           # regular expressions
import collections  # specialized container types

Practical Script Examples

Example 1: Word Counter

PYTHON

from collections import Counter

def count_words(filename):
    """Count word frequency in a text file."""
    with open(filename) as f:
        words = f.read().lower().split()
    counts = Counter(words)
    for word, count in counts.most_common(10):
        print(f"{word}: {count}")

count_words("my_text.txt")

Example 2: Simple CSV Processor

PYTHON

import csv

def process_csv(input_file, output_file):
    """Read a CSV, filter rows, and write results."""
    with open(input_file) as infile, open(output_file, "w", newline="") as outfile:
        reader = csv.DictReader(infile)
        fieldnames = reader.fieldnames
        writer = csv.DictWriter(outfile, fieldnames=fieldnames)
        writer.writeheader()

        for row in reader:
            if int(row["score"]) >= 80:
                writer.writerow(row)

process_csv("students.csv", "passing_students.csv")

Example 3: File Organizer

PYTHON

from pathlib import Path
import shutil

def organize_files(directory):
    """Sort files into folders by extension."""
    folder = Path(directory)
    for file in folder.iterdir():
        if file.is_file():
            ext = file.suffix.lower().lstrip(".")
            dest = folder / ext
            dest.mkdir(exist_ok=True)
            shutil.move(str(file), str(dest / file.name))

organize_files("~/Downloads")

Tips for Beginners

Best Practices

Use descriptive names: user_count not uc
Follow PEP 8: Python's official style guide
Use f-strings: Cleaner than .format() or % formatting
Prefer with for files: Automatic resource cleanup
Use list comprehensions: More Pythonic than manual loops for transforms
Start with the standard library: It covers most common needs

Common beginner mistakes: using mutable default arguments (def f(items=[])), confusing == with is, forgetting that range() excludes the end value, and modifying a list while iterating over it.

Next Steps

Once you're comfortable with these fundamentals, explore:

Object-Oriented Programming — classes, inheritance, encapsulation
Virtual environments — python -m venv for project isolation
Package management — pip install and requirements.txt
Type hints — def greet(name: str) -> str: for better tooling
Testing — pytest for writing and running tests
Async Python — asyncio for concurrent I/O operations