Python Strings Explained — Creation, Indexing, Methods and Common Mistakes

# --- Three valid ways to create a string ---

# Single quotes — great for short strings with no apostrophes
first_name = 'Jordan'

# Double quotes — use this when your text contains an apostrophe
full_sentence = "Jordan's favourite language is Python."

# Triple quotes — spans multiple lines without any special characters
welcome_message = """
Welcome to TheCodeForge!
We're glad you're here.
Let's build something great.
"""

# type() confirms all three are the same data type
print(type(first_name))      # Shows the data type
print(type(full_sentence))   # Same type
print(type(welcome_message)) # Still the same type

# len() counts the total number of characters in a string
print(len(first_name))       # Counts every character including spaces
print(len(full_sentence))

# Printing each variable so you can see what is stored
print(first_name)
print(full_sentence)
print(welcome_message)

product_code = "TF-PYTHON-2024"

# --- Positive indexing (left to right, starting at 0) ---
first_char  = product_code[0]   # 'T' — index 0 is always the first character
third_char  = product_code[2]   # '-' — the hyphen after 'TF'

# --- Negative indexing (right to left, starting at -1) ---
last_char        = product_code[-1]   # '4' — always the final character
second_to_last   = product_code[-2]  # '2'

print("First character:", first_char)
print("Third character:", third_char)
print("Last character:", last_char)
print("Second to last:", second_to_last)

# --- Slicing: string[start:stop] — start is included, stop is excluded ---
prefix   = product_code[0:2]    # Characters at index 0 and 1 — 'TF'
language = product_code[3:9]    # Characters from index 3 up to (not including) 9
year     = product_code[10:]    # From index 10 to the end — omitting stop grabs everything remaining

print("\nPrefix:", prefix)
print("Language:", language)
print("Year:", year)

# --- Step: string[start:stop:step] ---
every_other = product_code[::2]     # Every second character from the whole string
reversed_code = product_code[::-1]  # step of -1 reverses the entire string

print("\nEvery other character:", every_other)
print("Reversed:", reversed_code)

# Simulating messy user input — extra spaces and inconsistent casing are common
raw_user_input = "   hello@thecodeforge.io   "
raw_tag_input  = "Python,Beginner,DataStructures,Tutorial"

# --- Cleaning whitespace ---
# strip() removes spaces (and newlines) from both ends — does NOT change original
cleaned_email = raw_user_input.strip()
print("Raw:", repr(raw_user_input))    # repr() shows us the spaces clearly
print("Cleaned:", repr(cleaned_email))

# --- Case conversion ---
greeting = "Good Morning, Codeforger!"
print("\nUppercase:", greeting.upper())  # All caps — useful for comparisons
print("Lowercase:", greeting.lower())  # All lower — standard for normalising input
print("Title case:", greeting.title()) # Every word capitalised

# --- Searching inside a string ---
article_title = "Python Strings Explained for Beginners"
print("\nContains 'Strings':", "Strings" in article_title)          # True — 'in' operator is the cleanest way
print("Starts with 'Python':", article_title.startswith("Python")) # True
print("Ends with 'Experts':", article_title.endswith("Experts"))   # False
print("Position of 'Strings':", article_title.find("Strings"))     # Returns the index; -1 if not found

# --- Replacing text ---
old_domain = "Contact us at support@oldsite.com for help."
new_domain = old_domain.replace("oldsite.com", "thecodeforge.io")  # Returns new string; original unchanged
print("\nUpdated:", new_domain)

# --- Splitting and joining ---
# split() breaks a string into a list wherever it finds the separator
tags = raw_tag_input.split(",")   # Split on commas — gives us a Python list
print("\nTags list:", tags)

# join() does the reverse — assembles a list of strings into one string
formatted_tags = " | ".join(tags)  # The string you call join() on is the separator
print("Formatted tags:", formatted_tags)

# --- Basic f-string: just wrap your variables in {} ---
player_name  = "Alex"
player_level = 42
player_score = 98750.5

# f before the quote activates f-string mode
# Python evaluates everything inside {} at runtime
basic_greeting = f"Welcome back, {player_name}! You are level {player_level}."
print(basic_greeting)

# --- Expressions inside f-strings --- you're not limited to plain variables
next_level    = player_level + 1
progress_note = f"Reach level {next_level} to unlock new abilities."
print(progress_note)

# --- Format specifiers: control how values are displayed ---
# :.2f means 'float, show exactly 2 decimal places'
formatted_score = f"Your score: {player_score:,.2f} points"
print(formatted_score)  # Comma as thousands separator, 2 decimal places

# :>10 means 'right-align in a field 10 characters wide' — useful for tables
for item, cost in [("Sword", 1200), ("Shield", 850), ("Potion", 25)]:
    print(f"  {item:<10} costs {cost:>6} gold")  # Left-align item, right-align cost

# --- Method calls work inside {} too ---
raw_username = "   codeforger_99   "
print(f"\nNormalised username: {raw_username.strip().lower()}")

# --- Older approaches for comparison — f-strings are cleaner ---
# Old way with + concatenation (fragile, verbose)
old_style = "Player: " + player_name + ", Level: " + str(player_level)

# Old way with .format() (cleaner than +, but f-strings are better)
format_style = "Player: {}, Level: {}".format(player_name, player_level)

print("\nOld style:", old_style)
print("Format style:", format_style)