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Week 7 - Iteration & Search

Objective:

  • Explore techniques for looping, searching, and applying counting operations on strings and files in Python.
  • Practice solving exercises to solidify understanding.

Loops and Strings

  • For Loop Basics:
    • Review for loops, particularly range for numerical iteration.
    • Example: Loop to display numbers 0 to 2 in one line. 
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      for i in range(3):
    print(i, end=' ')
  • Character Iteration in Strings:
    • Looping through characters in a string.
    • New Code Example: Using a loop to print only vowels in a word. 
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      word = "Gadsby"
for letter in word:
    if letter.lower() in 'aeiou':
        print(letter, end=' ')
  • Checking for Specific Characters:
    • Demonstrate a function has_letter(word, char) that checks for any character in a word. 
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      def has_letter(word, char):
    for letter in word:
        if letter.lower() == char.lower():
            return True
    return False
    • Test has_letter("Gadsby", "a") and has_letter("Gadsby", "e").

Reading Files and Word Lists

  • Using the open Function:
    • How to open, read, and loop through each line in a file.
  • Example Code: Count lines in words.txt. 
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    file_path = 'words.txt'
with open(file_path, 'r') as file:
    line_count = sum(1 for _ in file)
print("Number of lines:", line_count)
  • Using strip() for Clean Data:
    • Show how strip() removes whitespace, including newlines.
  • Practice Exercise: Write a function count_words(file_path) that reads each line, strips whitespace, and counts the total words.

Variable Updating

  • Basic Assignments vs. Updates:
    • Difference between initializing, updating, and incrementing variables.
  • Example: Cumulative word length calculator for words with an “e”. 
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    def cumulative_length_e_words(file_path):
    total_length = 0
    with open(file_path, 'r') as file:
        for line in file:
            word = line.strip()
            if 'e' in word:
                total_length += len(word)
    return total_length
    • Test this function with a small word list.

Looping and Counting Patterns

  • Counter Variables:
    • Using counters to count specific conditions within loops.
  • Code Example: Count words containing at least one vowel. 
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    def count_vowel_words(file_path):
    count = 0
    with open(file_path, 'r') as file:
        for line in file:
            word = line.strip()
            if any(vowel in word for vowel in 'aeiou'):
                count += 1
    return count

Using the in Operator

  • Simplify Checks:
    • Rewrite has_letter using in. 
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      def has_letter(word, char):
    return char.lower() in word.lower()
  • Practice Excercise: Refactor a function that checks if a word contains any vowels using in.
  • Definition and Practicality:
    • Introduce linear search as a pattern that sequentially checks elements.
  • Example: General function contains_any(word, letters) using in. 
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    def contains_any(word, letters):
    return any(letter in word for letter in letters.lower())
  • Practice Exercise: Write a function to return all positions of a specified letter in a word.

Doctest and Testing Functions

  • Introduction to Doctests:
    • How doctests verify function correctness by embedding test cases in the docstring.
  • Example Code: Writing a doctest for the contains_any function. 
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    def contains_any(word, letters):
    """Checks if a word uses any letters in a given set.

    >>> contains_any('banana', 'aeiou')
    True
    >>> contains_any('banana', 'xyz')
    False
    """
    return any(letter in word for letter in letters.lower())
  • Practice Exercise: Write doctests for has_letter and run them.

Exercises

Exercise 1: Detect Palindromic Words

  • Write a function is_palindromic(word) that returns True if a word reads the same backward.

Exercise 2: Counting Words by Length

  • Write count_by_length(file_path, n) that counts the number of words with exactly n letters.

Exercise 3: Find Words with Specific Letter Patterns

  • Write find_words_with_pattern(file_path, pattern) to count words with a particular letter pattern.