Week 15 - Python Extras

Advanced Python Features

Learning Objectives

• Understand and apply Python sets for unique data manipulation and operations.
• Explore collections.Counter for counting elements and performing multiset operations.
• Learn to utilize defaultdict for simplifying dictionary initialization and handling missing keys.
• Use conditional expressions for concise code and logical branching.
• Master list comprehensions for creating lists efficiently.
• Understand any and all built-in functions for evaluating conditions across sequences.
• Familiarize with packing and unpacking keyword arguments for flexible function calls.

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1. Python Sets

Objective: Demonstrate set creation, operations, and practical applications.

Examples: 1. Creating and Manipulating Sets

fruits = set(['apple', 'orange', 'banana', 'apple'])  # Duplicates removed
print(fruits)  # {'orange', 'banana', 'apple'}

1. Set Operations
   

   evens = {2, 4, 6, 8}
   odds = {1, 3, 5, 7}
   primes = {2, 3, 5, 7}
   print(evens | odds)       # Union
   print(primes & evens)     # Intersection
   print(odds - primes)      # Difference
   print(odds <= primes)     # Subset
   

2. Practical Example
   Check if two lists share common elements:
   

   list1 = [1, 2, 3, 4]
   list2 = [3, 4, 5, 6]
   print(bool(set(list1) & set(list2)))  # True
   

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2. Using collections.Counter

Objective: Count elements in sequences and perform arithmetic operations.

Examples: 1. Counting Elements

from collections import Counter
votes = ['Alice', 'Bob', 'Alice', 'Alice', 'Bob']
count = Counter(votes)
print(count)  # Counter({'Alice': 3, 'Bob': 2})

1. Arithmetic Operations
   

   counter1 = Counter({'a': 3, 'b': 2})
   counter2 = Counter({'b': 1, 'c': 4})
   print(counter1 + counter2)  # Counter({'c': 4, 'a': 3, 'b': 3})
   print(counter1 - counter2)  # Counter({'a': 3, 'b': 1})
   

2. Anagram Checker
   

   def are_anagrams(word1, word2):
       return Counter(word1) == Counter(word2)
   print(are_anagrams('listen', 'silent'))  # True
   

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3. collections.defaultdict

Objective: Simplify dictionary initialization for dynamic values.

Examples: 1. Basic Usage

from collections import defaultdict
dd = defaultdict(int)
dd['a'] += 1
print(dd)  # defaultdict(<class 'int'>, {'a': 1})

1. Grouped Data
   

   names = [('USA', 'Alice'), ('USA', 'Bob'), ('India', 'Ravi')]
   grouped = defaultdict(list)
   for country, name in names:
       grouped[country].append(name)
   print(grouped)  # defaultdict(<class 'list'>, {'USA': ['Alice', 'Bob'], 'India': ['Ravi']})
   

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4. Conditional Expressions

Objective: Write concise conditional logic.

Examples: 1. Inline Logic

x = 10
y = 'Positive' if x > 0 else 'Negative'
print(y)  # Positive

1. Recursive Example
   

   def factorial(n):
       return 1 if n == 0 else n * factorial(n - 1)
   print(factorial(5))  # 120
   

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5. List Comprehensions

Objective: Simplify list construction.

Examples: 1. Simple Transformation

numbers = [1, 2, 3, 4]
squares = [n**2 for n in numbers]
print(squares)  # [1, 4, 9, 16]

1. Filter with Comprehension
   

   names = ['Alice', 'Bob', 'Charlie']
   short_names = [name for name in names if len(name) <= 4]
   print(short_names)  # ['Bob']
   

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6. Built-ins: any and all

Objective: Use these functions for efficient sequence checks.

Examples: 1. Using any

values = [0, 0, 1]
print(any(values))  # True

1. Using all
   

   values = [1, 1, 1]
   print(all(values))  # True
   

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7. Packing and Unpacking Keyword Arguments

Objective: Pass dynamic arguments to functions.

Examples: 1. Packing Arguments

def display_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")
display_info(name='Alice', age=25)

1. Unpacking into Function Calls
   

   data = {'name': 'Bob', 'age': 30}
   display_info(**data)
   

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Activities

1. Set Operations: Find common and unique elements between two lists.
2. Counter Applications: Write a program to count votes and find the winner.
3. Defaultdict Usage: Implement a function to group words by their first letter.
4. List Comprehensions: Create a list of even numbers from 1 to 20.
5. any and all: Check if a list contains only positive numbers.