Adding a new key:
user["email"] = "ahmed@gmail.com"
Updating an existing key:
user["age"] = 23
Deleting a key:
del user["city"]
user.pop("is_admin")
Checking if a key exists:
if "email" in user:
print("Has email")
print(len(user)) # number of keys
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user = {"name": "Ahmed", "age": 22, "city": "Dubai"}
# loop through keys only
for key in user:
print(key)
# loop through values only
for value in user.values():
print(value)
# loop through both — most useful
for key, value in user.items():
print(f"{key}: {value}")Output of last loop:
name: Ahmed
age: 22
city: Dubai
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Dictionaries can contain other dictionaries
This is how real user data is usually structured
users = {
"ahmed": {
"age": 22,
"is_admin": True
},
"sara": {
"age": 19,
"is_admin": False
}
}
print(users["ahmed"]["age"]) # 22
print(users["sara"]["is_admin"]) # FalseYou will see this exact pattern constantly when working with APIs and bots
Telegram sends you user data in this format
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A set is like a list but:
tags = {"python", "bots", "coding", "python"} # duplicate python
print(tags) # {'python', 'bots', 'coding'} — duplicate removedMost common use case — removing duplicates from a list:
numbers = [1, 2, 2, 3, 3, 3, 4]
unique = list(set(numbers))
print(unique) # [1, 2, 3, 4]
Checking membership is also faster with sets than lists
Use sets when you need unique items and do not care about order
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Watch this after reading through all the posts
Python Full Course 2024 — freeCodeCamp
Covers dictionaries, iterating over dictionaries, and associating values
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Build a simple contacts manager using a dictionary:
contacts = {
"Ahmed": "050-1234567",
"Sara": "055-7654321",
"Ali": "052-1112233"
}
# print all contacts
for name, number in contacts.items():
print(f"{name}: {number}")
# search for a contact
search = input("Search name: ").strip().title()
if search in contacts:
print(f"Number: {contacts[search]}")
else:
print("Contact not found")Extend it — let the user add a new contact and delete one
Screenshot your output
Bonus — store each contact as a nested dict with number and email
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You have been writing code that runs top to bottom
But what happens when you need to do the same thing in 10 different places?
You do not copy paste it 10 times
You put it in a function and call it whenever you need it
Functions are one of the most important concepts in programming
Everything in real code is built with functions
This lecture covers:
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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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