python.md

Python Summary

1. Setup

1.1. Download

Run python3 to check if it's already on your machine

• Mac: Run this in terminal: brew install python.
• Windows: Download the installer from python.org.
• Linux: Run this in terminal sudo apt-get install python3.

1.2. Run First Program

Create a file hello.py with the following content:

print("Hello, World!")

Run it using the command: python3 hello.py.

2. Main Functionality

2.1. Variable Types & Initialization

You don't need to set data type for Python variables explicitly, you just set a value to it.

str_var = "Hello"           # String
int_var = 42                 # Integer
float_var = 2.3             # Float
bool_var = True             # Boolean

list_var = [1, 2, 3]                                            # List(similar to arrays)
tuple_var = ("Hello", 42, True, 5.9, 66)              #Tuples (unchangable list)
set_var = {"Cairo", "London", "Paris"}                  # Set (unique values)
dict_var = {"key1": "value2", "key2": "value2"}         # Dictionary

null_var = None	    # Null value

Casting variables

int_var = int(2.8)      # 2
float_var = float("3.9")     #  3.9

2.2. Operators

• Arithmetic x = 5 * 2 - ( 3 + 1 )
• Assignment x += 1
• Logical x = not(True and (False or True))
• Comparison x >= 10

2.3. Function Definition

def greet(name):
    return "Hello, " + name

2.4. If & Conditions

• If else

if x > 10:
    print("x is greater than 10")
elif x == 10:
    print("x is 10")
else:
    print("x is less than 10")


# Short hand if
print("x is 10") if x == 10 else print("x is not 10")

• match case

char = 'e'
match char:
  case 'a':
    print("This character is a")
  case 'b':
    print("This character is b")
  case 'c' | 'd':
  	print("This character is c or d")
  case _:
    print("This character is not a , b , c nor d")

2.5. Loops

• loop on range

for i in range(5):  # For loop prints 0 to 4
    print(i)

• loop on array

cities = ["Cairo", "London", "Paris"]
for x in cities:
  print(x)

• loop on dictionary

dict =	{
  "key1": "value1",
  "key2": "value2"
}

for k, v in dict.items():
  print(k, "is", v)

• using continue

for x in range(0, 6):
  if x == 2:
    continue
  print(x) 
# prints 0 1 3 4 5

Catch Exception

try:
  doSomething()
except:
  print("Error occurred")
finally:
  print("Done")

3. Architecture

3.1. Importing Packages

from datetime import datetime, timedelta

current_datetime = datetime.now()

date_str = "2025-02-23 16:30:00"
parsed_datetime = datetime.strptime(date_str, "%Y-%m-%d %H:%M:%S")

old_date = parsed_datetime - timedelta(days=7)  

3.2. Classes & Dependencies

# file course.py
class Course:
    def __init__(self, name):
        self.name = name

    def __str__(self):
        return self.name

# file student.py
from course import Course  

class Student:
    def __init__(self, name):
        self.name = name
        self.courses = [] 

    def enroll(self, course):
        self.courses.append(course)
        print("Student:",  self.name, "enrolled in:", course)

    def list_courses(self):
            print("Student",  self.name,  "courses:", ' - '.join(course.name for course in self.courses))

# Example usage
if __name__ == "__main__":
    math = Course("Math")
    physics = Course("Physics")

    adam = Student("Adam")
    adam.enroll(math)      # Student: Adam enrolled in: Math
    adam.enroll(physics)   # Student: Adam enrolled in: Physics
    adam.list_courses()    # Student Adam courses: Math - Physics

4. Input & output

4.1. System Input

input_val = input("Choose number between 1 and 20:")

4.2. File Input

sample.txt

This is just
To test 
How read file in python works

my_file = open("sample.txt")
print("just 4 characters =>", my_file.read(4))
print("just one line => ", my_file.readline())
print("the whole file => ", my_file.read())
my_file.close()

Output

just 4 characters => This
just one line =>   is just

the whole file =>  To test 
How read file in python works

4.3. System output

print("Hello")              # Hello
print("Hello", "world") # Hello world

4.4. File output

my_file = open("sample.txt", "a")
my_file.write("This text will be added to the end of the file")
my_file.close()

my_file = open("sample.txt", "w")
my_file.write("This text will overwrite the contents of the file")
my_file.close()

5. Unit Tests

// todo add unit test example