strings.py

# String Concepts in Python

# ----------------------------------------------
# 1. INTRODUCTION TO STRINGS
# ----------------------------------------------

# A string is a sequence of characters enclosed in single (' '), double (" "), or triple quotes (''' ''' or """ """)
# Strings are immutable (cannot be changed once created)

# String examples
str1 = 'Hello'
str2 = "Python"
str3 = '''This is a 
multi-line string.'''

print("String 1:", str1)
print("String 2:", str2)
print("Multi-line String:\n", str3)


# ----------------------------------------------
# 2. STRING OPERATIONS
# ----------------------------------------------

# Concatenation (Joining Strings)
concat_str = str1 + " " + str2
print("\nConcatenated String:", concat_str)

# Repetition
repeat_str = str1 * 3
print("Repeated String:", repeat_str)

# Indexing (Accessing by position)
print("First character:", str1[0])
print("Last character:", str1[-1])

# Slicing (Extracting substring)
print("Sliced String (0 to 3):", str1[0:4])
print("Sliced String (from index 2):", str1[2:])
print("Sliced String (till index 3):", str1[:3])

# Length of string
print("Length of str2:", len(str2))

# Membership testing
print("'H' in str1:", 'H' in str1)
print("'z' not in str1:", 'z' not in str1)


# ----------------------------------------------
# 3. TRAVERSING A STRING
# ----------------------------------------------

# Traversing means accessing each character in a string, usually with a loop.

sample = "Python"

print("\nTraversing using for loop:")
for ch in sample:
    print(ch)

print("\nTraversing using index:")
for i in range(len(sample)):
    print("Character at index", i, ":", sample[i])


# ----------------------------------------------
# 4. STRING METHODS AND BUILT-IN FUNCTIONS
# ----------------------------------------------

# Common String Methods
text = "  Python Programming Language  "

print("\nOriginal Text:", text)

# Case conversion
print("Uppercase:", text.upper())
print("Lowercase:", text.lower())
print("Title Case:", text.title())
print("Swap Case:", text.swapcase())

# Whitespace removal
print("Stripped:", text.strip())

# Searching and replacing
print("Find 'Python':", text.find('Python'))
print("Replace 'Python' with 'Java':", text.replace('Python', 'Java'))

# Splitting and joining
words = text.split()  # splits string into list
print("Split into words:", words)
joined = "-".join(words)
print("Joined with '-':", joined)

# Counting and checking
print("Count of 'a':", text.count('a'))
print("Starts with 'Py':", text.strip().startswith("Py"))
print("Ends with 'age':", text.strip().endswith("age"))
print("Is Alphabetic:", text.strip().isalpha())  # returns False because spaces exist

# Built-in functions for strings
print("\nBuilt-in Functions:")
print("Length:", len(text))
print("Minimum character:", min(text))
print("Maximum character:", max(text))
print("Sorted characters:", sorted(text))


# ----------------------------------------------
# 5. HANDLING STRINGS
# ----------------------------------------------

# Since strings are immutable, modifications create new strings.

original = "Hello"
modified = original.replace("H", "J")

print("\nOriginal String:", original)
print("Modified String:", modified)

# String formatting
name = "Alice"
age = 21

# Using f-string (modern method)
info1 = f"My name is {name} and I am {age} years old."
print("\nFormatted (f-string):", info1)

# Using format() method
info2 = "My name is {} and I am {} years old.".format(name, age)
print("Formatted (format method):", info2)

# Escaping special characters
escaped = "This is a line break:\nNext line starts here."
print("\nEscaping Example:\n", escaped)

# Raw strings (ignore escape sequences)
raw = r"This is a raw string:\nNo new line"
print("Raw String Example:", raw)