Topic: Python Functions – Part 1 of 3: Basics, Syntax, and Parameters (Long Lesson)

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### 1. What is a Function in Python?

A function is a reusable block of code that performs a specific task. Functions help:

• Avoid code duplication
• Improve code readability
• Enable modular programming

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### 2. Why Use Functions?

• Reusability – Write once, use many times
• Modularity – Split large tasks into smaller blocks
• Debuggability – Easier to test/debug small units
• Abstraction – Hide complex logic behind a name

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### 3. Function Syntax

def function_name(parameters):
    # block of code
    return result

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### 4. Creating a Simple Function

def greet():
    print("Hello, welcome to Python functions!")
    
greet()  # Calling the function

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### 5. Function with Parameters

def greet_user(name):
    print(f"Hello, {name}!")

greet_user("Hussein")

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### 6. Function with Return Value

def add(a, b):
    return a + b

result = add(10, 5)
print(result)  # Output: 15

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### 7. Positional vs Keyword Arguments

def student_info(name, age):
    print(f"Name: {name}, Age: {age}")

student_info("Ali", 22)  # Positional
student_info(age=22, name="Ali")  # Keyword

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### 8. Default Parameter Values

def greet(name="Guest"):
    print(f"Hello, {name}!")

greet()            # Output: Hello, Guest!
greet("Hussein")   # Output: Hello, Hussein!

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### 9. Variable Number of Arguments

#### \*args – Multiple positional arguments:

def sum_all(*numbers):
    total = 0
    for num in numbers:
        total += num
    return total

print(sum_all(1, 2, 3, 4))  # Output: 10

#### \*\*kwargs – Multiple keyword arguments:

def print_details(**info):
    for key, value in info.items():
        print(f"{key}: {value}")

print_details(name="Ali", age=24, country="Egypt")

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### **10. Scope of Variables**

#### Local vs Global Variables

x = "global"

def func():
    x = "local"
    print(x)

func()     # Output: local
print(x)   # Output: global

Use global keyword if you want to modify a global variable inside a function.

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### 11. Docstrings (Function Documentation)

def square(n):
    """Returns the square of a number."""
    return n * n

print(square.__doc__)  # Output: Returns the square of a number.

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### 12. Best Practices

• Use descriptive names for functions
• Keep functions short and focused
• Avoid side effects unless needed
• Add docstrings for documentation

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### Exercise

• Create a function that takes a list and returns the average
• Create a function that takes any number of scores and returns the highest
• Create a function with default arguments for greeting a user by name and language

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#Python #Functions #CodingBasics #ModularProgramming #CodeReuse #PythonBeginners

https://t.iss.one/DataScience4

#Python #Top60 #BuiltInFunctions

#1. print()
Prints the specified message to the screen.

print("Hello, World!")

Hello, World!

#2. len()
Returns the number of items in an object.

my_list = [1, 2, 3, 4]
print(len(my_list))

4

#3. type()
Returns the type of an object.

name = "Python"
print(type(name))

<class 'str'>

#4. input()
Allows user input.

username = input("Enter your name: ")
print("Hello, " + username)

Enter your name: Alex
Hello, Alex

#5. int()
Converts a value to an integer number.

string_number = "101"
number = int(string_number)
print(number + 9)

110

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#Python #DataTypes #Conversion

#6. str()
Converts a value to a string.

age = 25
print("My age is " + str(age))

My age is 25

#7. float()
Converts a value to a floating-point number.

integer_value = 5
print(float(integer_value))

5.0

#8. bool()
Converts a value to a Boolean (True or False).

print(bool(1))
print(bool(0))
print(bool("Hello"))
print(bool(""))

True
False
True
False

#9. list()
Converts an iterable (like a tuple or string) to a list.

my_tuple = (1, 2, 3)
my_list = list(my_tuple)
print(my_list)

[1, 2, 3]

#10. tuple()
Converts an iterable to a tuple.

my_list = [4, 5, 6]
my_tuple = tuple(my_list)
print(my_tuple)

(4, 5, 6)

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#Python #Math #Functions

#11. sum()
Returns the sum of all items in an iterable.

numbers = [10, 20, 30]
print(sum(numbers))

60

#12. max()
Returns the largest item in an iterable.

numbers = [5, 29, 12, 99]
print(max(numbers))

99

#13. min()
Returns the smallest item in an iterable.

numbers = [5, 29, 12, 99]
print(min(numbers))

5

#14. abs()
Returns the absolute (positive) value of a number.

negative_number = -15
print(abs(negative_number))

15

#15. round()
Rounds a number to a specified number of decimals.

pi = 3.14159
print(round(pi, 2))

3.14

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#Python #Iterables #Functions

#16. range()
Returns a sequence of numbers, starting from 0 by default, and increments by 1.

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

0
1
2
3
4

#17. sorted()
Returns a new sorted list from the items in an iterable.

unsorted_list = [3, 1, 4, 1, 5, 9]
sorted_list = sorted(unsorted_list)
print(sorted_list)

[1, 1, 3, 4, 5, 9]

#18. enumerate()
Returns an enumerate object, which contains pairs of index and value.

fruits = ['apple', 'banana', 'cherry']
for index, fruit in enumerate(fruits):
    print(index, fruit)

0 apple
1 banana
2 cherry

#19. zip()
Returns an iterator that aggregates elements from two or more iterables.

names = ['Alice', 'Bob', 'Charlie']
ages = [25, 30, 35]
for name, age in zip(names, ages):
    print(f"{name} is {age} years old.")

Alice is 25 years old.
Bob is 30 years old.
Charlie is 35 years old.

#20. map()
Applies a given function to each item of an iterable and returns a map object.