You create a function with the def keyword:
def greet():
print("Hello! Welcome to the channel")
Nothing happens yet — you need to call it:
greet() # Hello! Welcome to the channel
greet() # Hello! Welcome to the channel
greet() # Hello! Welcome to the channel
One function, called 3 times
If you need to change the message you change it in one place — not 3
This is the power of functions
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Parameters let you pass data into a function:
def greet(name):
print(f"Hello {name}!")
greet("Ahmed") # Hello Ahmed!
greet("Sara") # Hello Sara!
greet("Ali") # Hello Ali!
Multiple parameters:
def introduce(name, age, city):
print(f"My name is {name}, I am {age} years old and from {city}")
introduce("Ahmed", 22, "Dubai")
Parameter = the variable in the function definition
Argument = the actual value you pass when calling it
People use these words interchangeably — do not stress about it
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Functions can also give something back using return
def add(a, b):
return a + b
result = add(10, 5)
print(result) # 15
Without return your function does something but gives nothing back
With return your function produces a value you can use elsewhere
def is_adult(age):
if age >= 18:
return True
return False
if is_adult(20):
print("Access granted")
else:
print("Access denied")
Return also stops the function immediately
Any code after return does not run
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You can give parameters a default value
If nothing is passed — it uses the default
def greet(name, message="Welcome back"):
print(f"Hello {name}! {message}")
greet("Ahmed") # Hello Ahmed! Welcome back
greet("Sara", "You are now banned") # Hello Sara! You are now banned
Default parameters must always come after non-default ones
You will use this constantly in bot handlers
For example a send_message function where parse_mode defaults to HTML
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Sometimes you do not know how many arguments will be passed
*args — accepts any number of positional arguments as a tuple:
def add_all(*numbers):
return sum(numbers)
print(add_all(1, 2, 3)) # 6
print(add_all(1, 2, 3, 4, 5)) # 15
**kwargs — accepts any number of keyword arguments as a dictionary:
def show_info(**details):
for key, value in details.items():
print(f"{key}: {value}")
show_info(name="Ahmed", age=22, city="Dubai")
You do not need to memorize these right now
Just know they exist — you will see them when reading library code
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Watch this after reading through all the posts
Python Full Course 2024 — freeCodeCamp
Covers creating custom functions, parameters, default values, and organizing code
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Build a calculator using functions:
def add(a, b):
return a + b
def subtract(a, b):
return a - b
def multiply(a, b):
return a * b
def divide(a, b):
if b == 0:
return "Cannot divide by zero"
return a / b
a = float(input("First number: "))
b = float(input("Second number: "))
op = input("Operation (+, -, *, /): ")
if op == "+":
print(add(a, b))
elif op == "-":
print(subtract(a, b))
elif op == "*":
print(multiply(a, b))
elif op == "/":
print(divide(a, b))
else:
print("Invalid operation")
Screenshot your output with a few different calculations
Bonus — wrap the whole thing in a loop so it keeps running until user types "exit"
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Your code will crash
Not maybe — definitely
The question is whether your program handles it gracefully or just dies
Error handling is what separates beginner code from production code
Real apps never crash on the user — they catch errors and respond properly
This lecture covers:
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When Python cannot run your code it raises an exception
By default this crashes your program with an error message
Common errors you have probably already seen:
print(x) # NameError — x does not exist
int("hello") # ValueError — cannot convert "hello" to int
10 / 0 # ZeroDivisionError — cannot divide by zero
my_list[99] # IndexError — index out of range
user["email"] # KeyError — key does not exist in dict
Each error type tells you exactly what went wrong
Read your error messages — they are your friend, not your enemy
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Wrap risky code in a try block
If it crashes Python jumps to the except block instead of dying
try:
age = int(input("Enter your age: "))
print(f"You are {age} years old")
except:
print("That is not a valid number")
Now if the user types "hello" instead of a number
Your program does not crash — it prints the error message and continues
Always catch specific exceptions when you can:
try:
age = int(input("Enter your age: "))
print(f"You are {age} years old")
except ValueError:
print("Please enter a number, not text")
Catching specific errors makes your code cleaner and easier to debug
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else — runs only if no exception occurred:
try:
age = int(input("Enter your age: "))
except ValueError:
print("Invalid input")
else:
print(f"Age saved: {age}") # only runs if try succeeded
finally — always runs no matter what:
try:
result = 10 / 0
except ZeroDivisionError:
print("Cannot divide by zero")
finally:
print("This always runs") # cleanup code goes here
finally is used for cleanup — closing files, closing database connections
You will use it a lot in bot development
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try:
number = int(input("Enter a number: "))
result = 100 / number
print(f"Result: {result}")
except ValueError:
print("That is not a number")
except ZeroDivisionError:
print("Cannot divide by zero")
except Exception as e:
print(f"Something went wrong: {e}") # catches anything else
Exception as e gives you the actual error message as a variable
Useful for logging what went wrong
Order matters — put specific exceptions first, general ones last
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You can also trigger errors yourself using raise
Useful when you want to enforce rules in your functions
def set_age(age):
if age < 0:
raise ValueError("Age cannot be negative")
if age > 150:
raise ValueError("That age is not realistic")
return age
try:
set_age(-5)
except ValueError as e:
print(f"Error: {e}")
This is how you protect your functions from bad input
You will use this pattern constantly in bot command handlers
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Watch this after reading through all the posts
Python Full Course 2024 — freeCodeCamp
Covers exceptions, try/except, handling specific errors, and abstracting user input
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Take the calculator from last lecture and add proper error handling:
def divide(a, b):
if b == 0:
raise ValueError("Cannot divide by zero")
return a / b
while True:
try:
a = float(input("First number: "))
b = float(input("Second number: "))
op = input("Operation (+, -, *, /): ")
if op == "+":
print(a + b)
elif op == "-":
print(a - b)
elif op == "*":
print(a * b)
elif op == "/":
print(divide(a, b))
else:
print("Invalid operation")
except ValueError as e:
print(f"Error: {e}")
except Exception as e:
print(f"Something went wrong: {e}")
Test it with bad inputs — letters, division by zero, invalid operators
Make sure it never crashes — just shows an error and continues
Screenshot your output
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You have been writing everything from scratch
But Python comes with thousands of pre-built tools ready to use
You just need to know how to import them
This lecture covers:
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A module is just a Python file with functions and variables inside it
A library is a collection of modules
Instead of writing everything yourself you import code others already wrote
This is how real development works — nobody builds from scratch every time
import math # built-in Python module
print(math.pi) # 3.141592653589793
print(math.sqrt(16)) # 4.0
print(math.floor(4.9)) # 4
print(math.ceil(4.1)) # 5
You can also import specific things from a module:
from math import sqrt, pi
print(sqrt(25)) # 5.0 — no need to write math.sqrt
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random — generating random values:
import random
print(random.randint(1, 10)) # random number 1-10
print(random.choice(["a", "b", "c"])) # random item from list
random.shuffle([1, 2, 3, 4, 5]) # shuffles a list
datetime — working with dates and times:
from datetime import datetime
now = datetime.now()
print(now) # current date and time
print(now.strftime("%d/%m/%Y")) # formatted: 01/01/2025
print(now.strftime("%H:%M:%S")) # formatted: 14:30:00
os — interacting with the operating system:
import os
print(os.getcwd()) # current working directory
os.makedirs("my_folder") # create a folder
print(os.listdir(".")) # list files in current directory
json — working with JSON data:
import json
data = {"name": "Ahmed", "age": 22}
json_string = json.dumps(data) # dict to JSON string
print(json_string)
back_to_dict = json.loads(json_string) # JSON string to dict
print(back_to_dict["name"])
You will use json constantly with Telegram bots — Telegram talks in JSON
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pip is Python's package manager — it downloads and installs libraries for you
Open your terminal and run:
pip install requests
Then use it in your code:
import requests
response = requests.get("https://api.github.com")
print(response.status_code) # 200 means success
print(response.json()) # the actual data
requests lets you fetch data from the internet
This is how your bot will talk to external APIs later
Other libraries you will install soon:
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