: View of values.

my_dict.items(): View of key-value pairs.

my_dict.get("key", default): Get value safely.

pop("key"): Remove and return value.

4.4. Sets (Mutable, Unordered, Unique Elements)

Definition: my_set = {1, 2, 3}, set([1, 2, 2]) -> {1, 2}
Methods:
- add(item)
- remove(item)
- union(), intersection(), difference()

5. Functions

Definition:

def greet(name):
  return f"Hello, {name}!"

greet("Bob") # -> "Hello, Bob!"

Parameters:
- Default values: def func(a, b=1):
- Arbitrary arguments: def func(*args): (tuple)
- Arbitrary keyword arguments: def func(**kwargs): (dict)

Lambda Functions (Anonymous):

add = lambda x, y: x + y
add(2, 3) # -> 5

6. Classes & Objects (OOP)

Definition:

class Dog:
  def __init__(self, name, age):
    self.name = name
    self.age = age

  def bark(self):
    return f"{self.name} says Woof!"

my_dog = Dog("Buddy", 3)
my_dog.bark() # -> "Buddy says Woof!"

Inheritance:

class Poodle(Dog):
  def __init__(self, name, age, color):
    super().__init__(name, age)
    self.color = color

7. Modules & Packages

Importing:

import math
print(math.pi)

from datetime import date
today = date.today()

import pandas as pd

8. File I/O

Reading a file:

with open("file.txt", "r") as f:
  content = f.read()     # read all
  lines = f.readlines()  # read all lines into a list
  for line in f:         # iterate line by line
    print(line)

Writing to a file:

with open("output.txt", "w") as f: # "a" for append
  f.write("Hello, Python!\n")
  f.writelines(["Line 1\n", "Line 2\n"])

9. Error Handling

Try/Except:

try:
  result = 10 / 0
except ZeroDivisionError:
  print("Cannot divide by zero!")
except Exception as e:
  print(f"An error occurred: {e}")
else:
  print("No error occurred.")
finally:
  print("This always executes.")

10. String Formatting

f-strings (Python 3.6+):

name = "Charlie"
age = 25
print(f"Name: {name}, Age: {age}")
pi = 3.14159
print(f"Pi: {pi:.2f}") # -> Pi: 3.14

.format() method:

"Name: {}, Age: {}".format(name, age)
"Name: {0}, Age: {1}".format(name, age)
"Name: {n}, Age: {a}".format(n=name, a=age)

11. List Comprehensions

Creating lists concisely:

squares = [x**2 for x in range(5)] # -> [0, 1, 4, 9, 16]
evens = [x for x in range(10) if x % 2 == 0] # -> [0, 2, 4, 6, 8]

12. Common Built-in Functions

len(obj): Length of sequence/collection.
print(*args): Output to console.
input(prompt): Get user input.
range(stop), range(start, stop), range(start, stop, step)
map(func, iterable): Apply func to all items.