Python: Basics of Strings

# Strings can be created in several ways

# 1. Using single quotes
name = 'Alice'
greeting = 'Hello, World!'
print(greeting)  # Hello, World!

# 2. Using double quotes
message = "Python is awesome"
print(message)  # Python is awesome

# 3. Single quotes vs double quotes
# You can use either, but be consistent
# Use double quotes when your string contains single quotes:
text = "It's a beautiful day"
print(text)  # It's a beautiful day

# Use single quotes when your string contains double quotes:
quote = 'She said, "Hello!"'
print(quote)  # She said, "Hello!"

# 4. Triple quotes for multi-line strings
long_text = """This is a multi-line string.
It can span multiple lines.
You can write paragraphs in it."""
print(long_text)

# 5. Triple quotes with single quotes work too
another_text = '''This is also a multi-line string.
It works the same way.'''

# 6. Creating empty strings
empty1 = ''
empty2 = ""
empty3 = str()  # Using the str() function
print(empty1)  # (nothing prints)

# 7. Converting other types to strings
age = 25
age_str = str(age)
print(f"Age as string: {age_str}")
print(f"Type: {type(age_str)}")

# Each character in a string has an index (position)

word = "Python"

# 1. Positive indexing (starts from 0)
print(word[0])  # P
print(word[1])  # y
print(word[2])  # t
print(word[3])  # h
print(word[4])  # o
print(word[5])  # n

# 2. Negative indexing (starts from -1 from the end)
print(word[-1])  # n
print(word[-2])  # o
print(word[-3])  # h
print(word[-4])  # t
print(word[-5])  # y
print(word[-6])  # P

# 3. Getting the length of a string
length = len(word)
print(f"Length of '{word}': {length}")  # 6

# 4. Accessing the last character
last_char = word[-1]  # or word[len(word)-1]
print(f"Last character: {last_char}")

# 5. Trying to access an index that doesn't exist
# print(word[10])  # This will cause an IndexError

# 6. Strings are sequences - you can check if a character exists
if 'P' in word:
    print("'P' is in the string")

# Slicing lets you extract a portion of a string
# Syntax: string[start:end:step]

text = "Python Programming"

# 1. Basic slicing
print(text[0:6])   # Python (characters from index 0 to 5)
print(text[7:18])  # Programming (index 7 to 17)
print(text[:6])    # Python (from beginning to index 5)
print(text[7:])    # Programming (from index 7 to end)
print(text[:])     # Python Programming (entire string)

# 2. Slicing with negative indices
print(text[-11:])  # Programming (from -11 to end)
print(text[-6:-1])  # rammi (last 5 characters except the last)

# 3. Slicing with step
word = "abcdefghij"
print(word[::2])   # acegi (every second character)
print(word[1::2])  # bdfhj (every second character starting from index 1)
print(word[::-1])  # jihgfedcba (reverses the string)

# 4. Practical examples
name = "Alice Johnson"
first_name = name[:5]
last_name = name[6:]
print(f"First name: {first_name}")  # Alice
print(f"Last name: {last_name}")    # Johnson

# 5. Slicing to get a substring
email = "user@example.com"
username = email[:email.index('@')]
domain = email[email.index('@')+1:]
print(f"Username: {username}")  # user
print(f"Domain: {domain}")      # example.com

# Concatenation means joining strings together

# 1. Using the + operator
first_name = "Alice"
last_name = "Johnson"
full_name = first_name + " " + last_name
print(full_name)  # Alice Johnson

# 2. Joining multiple strings
greeting = "Hello"
name = "Bob"
message = greeting + ", " + name + "!"
print(message)  # Hello, Bob!

# 3. Concatenating string literals
# Python automatically concatenates adjacent string literals
text = "Hello" " " "World"
print(text)  # Hello World

# 4. Using join() method (more efficient for many strings)
words = ["Python", "is", "awesome"]
sentence = " ".join(words)
print(sentence)  # Python is awesome

# 5. Concatenating numbers (must convert to string first)
age = 25
message = "I am " + str(age) + " years old"
print(message)  # I am 25 years old

# 6. Using f-strings (Python 3.6+)
name = "Charlie"
age = 30
message = f"{name} is {age} years old"
print(message)  # Charlie is 30 years old

# The * operator repeats strings

# 1. Basic repetition
text = "Ha"
print(text * 3)  # HaHaHa

# 2. Creating a line
line = "-" * 40
print(line)
print("Header")
print(line)

# 3. Creating a pattern
pattern = "* " * 10
print(pattern)  # * * * * * * * * * *

# 4. Repeating with variables
count = 5
print("Hello " * count)  # Hello Hello Hello Hello Hello

# 5. Repeating zero times gives an empty string
print("Test" * 0)  # (nothing prints)

# 6. Repeating with user input
# num = int(input("How many times? "))
# print("Yes! " * num)

# 7. Creating a simple progress bar
def progress_bar(percentage):
    filled = "█" * (percentage // 10)
    empty = "░" * (10 - (percentage // 10))
    return f"{filled}{empty} {percentage}%"

print(progress_bar(30))  # ███░░░░░░░ 30%
print(progress_bar(75))  # ███████░░░ 75%

# Strings in Python are immutable — they cannot be changed after creation

text = "Hello"

# 1. Trying to change a character directly (this doesn't work)
# text[0] = "J"  # This will cause a TypeError

# 2. Instead, you create a new string
new_text = "J" + text[1:]
print(new_text)  # Jello

# 3. Converting to a list (mutable), changing, then back to string
text_list = list("Hello")
text_list[0] = "J"
new_text = "".join(text_list)
print(new_text)  # Jello

# 4. Many string methods return new strings
original = "python"
upper_version = original.upper()
print(original)     # python (unchanged)
print(upper_version) # PYTHON (new string)

# 5. Memory efficiency
# Python reuses strings when possible
a = "hello"
b = "hello"
print(a is b)  # True (same object in memory)

# 6. Each modification creates a new string
text = "Hello"
text = text + " World"  # Creates a new string, old one is garbage collected

# Escape sequences let you include special characters in strings

# 1. Newline (\n)
print("Hello\nWorld")
# Hello
# World

# 2. Tab (\t)
print("Name:\tAlice")
print("Age:\t25")
# Name:   Alice
# Age:    25

# 3. Backslash (\\)
print("C:\\Users\\Documents")
# C:\Users\Documents

# 4. Single quote (\')
print("It\'s a beautiful day")
# It's a beautiful day

# 5. Double quote (\")
print("She said, \"Hello!\"")
# She said, "Hello!"

# 6. Raw strings (ignore escape sequences)
path = r"C:\Users\Documents\file.txt"
print(path)  # C:\Users\Documents\file.txt

# 7. Unicode characters
print("\u263A")  # ☺
print("\u2764")  # ❤

# 8. Combining escape sequences
print("Line1\nLine2\nLine3")
print("Column1\tColumn2\tColumn3")