python basic code

 

Python A–Z — 01 Basics

Beginner problems with answers. Copy any code and run in your IDE.

1) Print Hello World

Output Print text to console.

print("Hello, World!")

2) Comments (Single & Multi-line)

Syntax Explain your code.

# This is a single-line comment
""" 
This is a multi-line comment / docstring.
Use it for module, function, or class docs.
"""

3) Variables & Basic Data Types

Types int, float, str, bool.

# Creating variables
age = 21                  # int
height = 1.72             # float
name = "Indranil"         # str
is_student = True         # bool

print(type(age), type(height), type(name), type(is_student))

4) Take User Input (str, int, float)

Input Convert using int()/float().

name = input("Your name: ")             # str
age = int(input("Your age: "))          # int
score = float(input("Your score: "))    # float
print(f"Hi {name}! Age: {age}, Score: {score}")

5) Type Casting

Casting Convert between types.

a = "25"
print(int(a) + 5)   # 30
print(str(99) + " bottles")
print(bool(0), bool(3), bool(""), bool("x"))

6) Arithmetic Operators

Operators + - * / // % **

a, b = 7, 3
print(a + b, a - b, a * b)
print(a / b)     # true division
print(a // b)    # floor division
print(a % b)     # remainder
print(a ** b)    # power

7) Assignment Operators

Operators Update variable values.

x = 10
x += 5   # 15
x *= 2   # 30
x //= 3  # 10
print(x)

8) Relational & Logical Operators

Logic and / or / not

a, b = 5, 9
print(a < b, a == b, a != b)     # True, False, True
print(a < b and b < 10)          # True
print(a > b or a == 5)           # True
print(not (a == 5))              # False

9) If / Else (Decision Making)

Control Branching.

n = int(input("Number: "))
if n > 0:
    print("Positive")
elif n < 0:
    print("Negative")
else:
    print("Zero")

10) One-Line If (Ternary)

Control Short decision.

n = int(input("N: "))
print("Even" if n % 2 == 0 else "Odd")

11) For Loop with range()

Loop Counting from 0..4

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

12) While Loop (Countdown)

Loop Repeat until condition false.

n = 3
while n > 0:
    print(n)
    n -= 1

13) break / continue / pass

Loop Control statements.

for x in range(10):
    if x == 5:
        break          # stop loop
    if x % 2:
        continue       # skip odds
    print(x)

if True:
    pass               # placeholder

14) String Basics & Slicing

Strings slice, len, case.

s = "hello python"
print(len(s))          # 12
print(s[:5])           # hello
print(s.upper())       # HELLO PYTHON
print(s.find("py"))   # 6

15) f-Strings (Formatting)

Strings easy string templates.

name = "Riya"
score = 95.678
print(f"{name} scored {score:.2f}")   # Riya scored 95.68

16) Lists — Create & Modify

List CRUD operations.

a = [10, 30, 20]
a.append(40)
a.insert(1, 99)
a.remove(20)
last = a.pop()
a.sort()
print(a, last)

17) Tuple & Unpacking

Tuple immutable sequence.

pt = (10, 20)
x, y = pt
print(x, y)

18) Dictionary — CRUD & Access

Dict key → value mapping.

user = {"name":"Ana","age":21}
user["city"] = "Kolkata"
print(user.get("name"))
print(list(user.keys()))
user.update({"age":22})
print(user)

19) Set — Unique Elements

Set no duplicates.

s = {1,2,2,3}
s.add(4)
s.discard(2)
print(s, 3 in s)

20) List Comprehension (Squares & Evens)

Comprehension concise list build.

squares = [x*x for x in range(6)]
ev = [x for x in range(10) if x % 2 == 0]
print(squares, ev)

21) Define Function + Default Arg

Functions reuse logic.

def greet(name="friend"):
    return f"Hello, {name}!"

print(greet("Rahul"))
print(greet())

22) Lambda (Small Function)

Functions short inline function.

add = lambda a,b: a+b
print(add(2,3))

23) Try / Except (Handle Errors)

Errors graceful failure.

try:
    x = int(input("Number: "))
    print(10 / x)
except ZeroDivisionError:
    print("Cannot divide by zero")
except ValueError:
    print("Please enter a valid number")

24) File Write & Read

Files with open(...)

with open("sample.txt","w") as f:
    f.write("Hello file!\n")

with open("sample.txt") as f:
    print(f.read())

25) Using math Module

Modules import & use.

import math
print(math.sqrt(16), math.pi)

26) Mini: Simple Calculator (Two Numbers)

Mini operations on a & b.

a = float(input("A: "))
b = float(input("B: "))
print("+:", a+b)
print("-:", a-b)
print("*:", a*b)
print("/:", a/b if b!=0 else "Infinity")

27) Swap Two Numbers (No Temp)

Basics tuple unpacking.

a, b = 3, 5
a, b = b, a
print(a, b)

28) Largest of Two Numbers

Practice conditional expression.

a = int(input("A: "))
b = int(input("B: "))
print(a if a > b else b)

29) Sum of Numbers from One Line Input

Practice split → map → sum.

nums = list(map(int, input("Enter numbers: ").split()))
print(sum(nums))

30) Filter Evens from List (Comprehension)

Comprehension simple filter.

nums = [1,2,3,4,5,6]
ev = [x for x in nums if x % 2 == 0]
print(ev)

End of Basics • Next file: Operators