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Python Conditional Statements

This Python code demonstrates basic conditional statements (if, elif, else) and introduces a newer pattern-matching approach (match-case) for handling specific conditions, often preferred in Python 3.10 and later.

If and else

Checking If a Number Is Positive, Negative, or Zero:

a = 5

if a > 0:
    print('The number is positive')
elif a < 0:
    print('The number is negative')
else:
    print('the number is zero')

Explanation:

  • This block of code checks whether the variable a is positive, negative, or zero using if, elif, and else statements.
  • The if condition checks if the number is greater than 0. If true, it prints "The number is positive".
  • If the number isn't positive, the elif condition checks if it's negative. If true, it prints "The number is negative".
  • If neither of the two conditions is true, the else statement is executed, printing "The number is zero".

Checking If It’s Raining:

is_raining = False 

if is_raining:
    print('Go out with an umbrella')
else:
    print('Go out freely it is a shinny day!')

Explanation:

  • This section checks the Boolean value is_raining.
  • If is_raining is True, it advises going out with an umbrella.
  • If is_raining is False, it prints a message suggesting going out freely because it’s a sunny day.

Weather Conditions Using if-elif-else:

weather = input('What is the weather today? ').lower()

if weather == 'rainy':
    print('Go with an unbrella or a raincoat')
elif weather == 'cloudy':
    print('It may rain and consider a raincoat')
elif weather == 'snowy':
    print('It may be slippery')
elif weather == 'foggy':
    print('Visiblity might be hindered')
elif weather == 'sunny':
    print('It is a great day to go to the beach')
else:
    print('No one knows about the weather')

print('test it')

Explanation:

  • This commented-out section (enclosed in triple quotes) takes the user's input for the weather and performs multiple checks using if-elif-else.
  • Based on the weather condition provided, it prints appropriate advice for going outside.

Match case

Weather Conditions Using match-case:

weather = input('What is the weather today? ').lower()
match weather:
    case 'rainy':
        print('Go with an unbrella or a raincoat')
    case 'cloudy':
        print('It may rain and consider a raincoat')
    case 'snowy':
        print('It may be slippery')
    case 'foggy':
        print('Visiblity might be hindered')
    case 'sunny':
        print('It is a great day to go to the beach')
    case _:
        print('No one knows about the weather')

Explanation:

  • This block uses the match-case structure, introduced in Python 3.10, which provides a more efficient and readable way to handle multiple conditions, replacing a chain of if-elif-else statements.
  • The match keyword checks the value of the weather variable and matches it against specific cases ('rainy', 'cloudy', etc.).
  • If no match is found, the default case (case _) is executed, printing "No one knows about the weather".

Key Takeaways:

  • Conditional Statements (if-elif-else): Useful for checking multiple conditions and executing different blocks of code based on those conditions.
  • Pattern Matching (match-case): A more modern and efficient way to handle conditions that involve multiple specific cases, improving readability, especially for many branches.

String and String Operations

  • A string is a sequence of characters enclosed within single, double, or triple quotes.
  • This documentation illustrates various string operations, slicing, methods, and formatting using Python.

Example: Basic String Declaration and Operations:

letter = 'a'
print(type(letter), len(letter))  # Output: <class 'str'> 1

alphabets = 'abcdefghijklmnopqrstuvwxyz'
print(alphabets, len(alphabets))  # Output: 'abcdefghijklmnopqrstuvwxyz', 26
print(list(alphabets))  # Converts the string into a list of characters

String Indexing

  • Python strings support indexing, allowing access to individual characters by their position.
lang = 'Python'
print(lang[0])  # Output: 'P'
print(lang[-1])  # Output: 'n'

String Slicing

  • Slicing allows for extracting a portion of the string.
print(lang[0:2])  # Output: 'Py' (slices from index 0 to 2, not including index 2)
print(lang[-4:-1])  # Output: 'tho' (slices from index -4 to -1)

String Methods

Python provides a variety of string methods for common tasks:

  • String Methods List:
    • 'capitalize', 'upper', 'lower', 'title', 'strip', 'replace', 'find', 'split', 'join', 'startswith', 'endswith' etc.
txt = 'Python for everyone'
print(txt.upper())  # Output: 'PYTHON FOR EVERYONE'
print(txt.lower())  # Output: 'python for everyone'
print(txt.capitalize())  # Output: 'Python for everyone'

String Formatting

  • Python provides several ways to format strings:

  1. Using + operator:

    full_name = first_name + ' ' + last_name
print(full_name)  # Concatenates strings

  2. Using format():

    print('I am {} {}. I am {} years old.'.format(first_name, last_name, age))

  3. Using f-strings:

    formated_string = f'I am {first_name} {last_name}. I teach {language}.'
print(formated_string)

Working with DNA Sequence (String Operations):

  • Count the occurrences of specific characters in a DNA string and calculate their frequency.
dna = '''CTAGCAAACTGCTGAT...'''  # (trimmed for brevity)
total = len(dna)
a = dna.count('A')
c = dna.count('C')
t = dna.count('T')
g = dna.count('G')
print(a / total, c / total, t / total, g / total)  # Output: Frequencies of A, C, T, G

Additional Examples:

  • String Replacement:

    print('I love people'.replace('love', 'like'))  # Output: 'I like people'

  • String Searching:

    txt = 'Python for everyone'
print(txt.find('y'))  # Output: 1 (position of first 'y')
print(txt.index('P'))  # Output: 0

Handling Large Texts

  • A sample speech from Donald Trump is processed by splitting it into words, converting them to lowercase, and removing punctuation.
  • Then, unique words are identified using a set.
donald_speech = '''Chief Justice Roberts, President...'''  # (trimmed for brevity)
words = donald_speech.lower().replace('–', ' ').replace('.', ' ').split()
unique_words = set(words)
print(len(unique_words))  # Output: Count of unique words

Conclusion

This document covers the basics of string manipulation in Python, including indexing, slicing, methods, and formatting techniques. These concepts are essential for processing text data efficiently in Python.

Python Lists

This document explains basic operations and methods related to lists in Python, including list creation, accessing elements, and using built-in list methods.

List Characteristics

  • A list is a collection of items, which are indexed and ordered.
  • Lists are mutable, meaning the elements can be changed after the list is created.

Creating an Empty List

You can create an empty list using the list() constructor.

empty_list = list()
print(len(empty_list), empty_list)  # Outputs the length and the empty list
print(type(empty_list))  # Shows the type as <class 'list'>
print(dir(empty_list))  # Lists all methods available for the list object

Common List Methods

A list of some of the most common list methods in Python:

lst_methods = ['append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

Accessing List Elements

A list of numbers is created. You can access elements using their index.

nums = [1, 2, 3, 4, 5]
print(nums, len(nums))  # Prints the list and its length
print(nums[0])  # Accesses the first element
print(nums[1])  # Accesses the second element
print(nums[4])  # Accesses the last element using its positive index

# Accessing the last element using negative indexing
print(nums[-1])

# Slicing the list
print(nums[1:4])  # Prints elements from index 1 to 3
print(nums[2:])  # Prints from index 2 to the end
print(nums[:3])  # Prints elements from the start to index 2

Modifying Lists

You can modify lists by adding, inserting, or removing elements.

Adding Elements

  • append(): Adds an item to the end of the list.
  • extend(): Adds multiple items to the list.
# nums.append(6)
# nums.extend([7, 8, 9, 10])

Removing Elements

  • pop(): Removes and returns an element at the given index. If no index is provided, it removes the last element.
  • del: Deletes an element or a slice of the list.
# nums.pop()  # Removes the last element
# nums.pop(0)  # Removes the first element
# del nums[4]  # Deletes the element at index 4

Inserting Elements

  • insert(): Inserts an item at a given position.
nums.insert(3, 333)  # Inserts 333 at index 3
nums.insert(6, 'the last item')  # Inserts a string at index 6

Counting and Reversing Elements

  • count(): Returns the count of occurrences of a value in the list.
  • reverse(): Reverses the order of the list.
countries = ['Finland', 'Finland', 'Finland', 'Denmark', 'Norway', 'Finland', 'Finland', 'Sweden']
print(countries.count('Finland'))  # Counts how many times 'Finland' appears

copy_lst = nums.copy()  # Copies the list
copy_lst.reverse()  # Reverses the copied list
print(copy_lst)

Sorting Lists

Lists can be sorted in ascending or descending order.

  • sort(): Sorts the list in place.
  • sorted(): Returns a sorted copy of the list.
new_num = [25, 20, 10, 3, 5, 0, 24]
print(sorted(new_num))  # Returns a sorted list in ascending order
print(sorted(new_num, reverse=False))  # Sorts without reversing

List Summary

This document covered the following list operations:

  • Creating and accessing elements in lists.
  • Adding, inserting, and removing elements.
  • Counting and reversing elements.
  • Sorting lists using sorted() and sort().

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