Day 3: Python Basics Cheatsheet

Python Basics Cheatsheet

Here's a summary of the Python basics, from data types and structures to commonly used functions.

Detailed Explanation of Python Basics

Here’s a deeper look at each element from the cheatsheet. These explanations and examples will make it easier to understand and use each concept as I continue my data science journey.

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Data Types

• int: Represents an integer value, used for whole numbers.

• float: Represents a floating-point number, used for numbers with decimals.

• str: Represents a string, used for sequences of characters.

• bool: Represents a boolean value, which can be either True or False.

    x = 5            # x is an integer with a value of 5
    y = 3.14         # y is a float with a value of 3.14
    name = "Alice"   # name is a string containing the text "Alice"
    is_valid = True  # is_valid is a boolean set to True
  

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Operators

• Arithmetic Operators: Used for basic mathematical operations.

• Comparison Operators: Used to compare two values and return a boolean result.

• Logical Operators: Used to combine multiple conditions.

    5 + 3           # adding numbers
    4 * 2           # multiplying numbers
    x > y           # checks if x is greater than y
    True and False  # evaluates to False since both conditions aren’t true
  

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Data Structures

• list: Ordered, mutable collection that can hold multiple items.

• tuple: Ordered, immutable collection, meaning items cannot be changed after creation.

• set: Unordered collection with unique items only, useful for removing duplicates.

• dict: Key-value pairs that allow fast lookups by keys, useful for structured data.

    # fruits is a list with three items
    fruits = ["apple", "banana", "cherry"]
  
    # point is a tuple representing coordinates
    point = (3, 5)
  
    # unique_nums is a set with three unique numbers
    unique_nums = {1, 2, 3}
  
    # person is a dictionary with name and age
    person = {"name": "Alice", "age": 25}
  

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Control Structures

• if, elif, else: Conditional statements to control program flow.

    if x > 5:
        print("High")
    elif x == 5:
        print("Equal")
    else:
        print("Low")
  

• for loop: Iterates over a sequence like a list or string.

    items = [1, 2, 3]
    for item in items:
        print(item)
  

• while loop: Repeats as long as a condition is True.

    x = 0
    while x < 5:
        print(x)
        x += 1
  

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Functions

• def: Used to define a function, which is a reusable block of code.

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

• lambda: Defines an anonymous function in a single line, often used for short functions.

    square = lambda x: x**2  # Defines a function that squares a number.
  

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Common Methods

• .append(): Adds an item to the end of a list.

    fruits = ["apple"]
    fruits.append("banana")
    print(fruits)  # Output: ["apple", "banana"]
  

• .remove(): Removes an item from a list.

    fruits = ["apple", "banana"]
    fruits.remove("apple")
    print(fruits)  # Output: ["banana"]
  

• .get(): Retrieves a value from a dictionary by its key.

    person = {"name": "Alice"}
    print(person.get("name"))  # Output: "Alice"
  

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Libraries

• import: Brings a library into the current script.

    import math
    print(math.sqrt(16))  # Output: 4.0
  

• math.sqrt(): Returns the square root of a number.

    math.sqrt(25)  # Output: 5.0
  

• random.choice(): Selects a random item from a list.

    import random
    fruits = ["apple", "banana", "cherry"]
    print(random.choice(fruits))  # Output could be "banana"
  

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File Handling

• open(): Opens a file, allowing reading or writing.

    file = open("data.txt", "r")
    content = file.read()
    file.close()
  

• with open(): Opens a file and ensures it is closed afterward.

    with open("data.txt", "r") as file:
        content = file.read()
  

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Exception Handling

• try, except, finally: Manages errors without crashing the program.

    try:
        x = 1 / 0
    except ZeroDivisionError:
        print("Cannot divide by zero")
  

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Basic Input/Output

• input(): Prompts the user to enter data.

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

• print(): Displays output on the screen.

    print("Hello, world!")
  

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Reflection on Day 3

Today’s exercise in summarizing Python basics into a single reference sheet felt like building a strong foundation. These basics will be invaluable in the days ahead, as they form the backbone of all data science projects.

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Thanks for following along! I’m excited to keep progressing in Python and getting one step closer to tackling real-world data problems. If you’re also on this journey or have resources to share, feel free to connect!