Strings: Working with Text

Text is everywhere

Names, messages, file contents, web pages, user input — a huge amount of real programming is just shuffling text around. Python's text type, the string, comes loaded with tools that make this genuinely pleasant. A string is any text inside quotes, single or double, it doesn't matter which:

greeting = "Hello"
name = 'Ahmedabad'

Use double quotes when your text contains an apostrophe ("it's a cat") and single quotes when it contains double quotes. For text spanning multiple lines, use triple quotes:

poem = """Roses are red,
Violets are blue,
Python is easy,
And so are you."""

Strings are sequences — indexing and slicing

A string is an ordered sequence of characters, and each character has a position number called an index, starting from zero. That zero trips up every beginner once, so burn it in: the first character is at index 0.

word = "PYTHON"
#       012345
print(word[0])    # P  (first character)
print(word[1])    # Y
print(word[-1])   # N  (negative counts from the end)
print(word[-2])   # O

You can grab a whole range of characters with slicing, using [start:stop]. The start is included, the stop is not:

word = "PYTHON"
print(word[0:3])   # PYT  (positions 0, 1, 2 — stop 3 excluded)
print(word[2:])    # THON (from 2 to the end)
print(word[:4])    # PYTH (from start up to 4)

This "stop is excluded" rule is consistent across all of Python — once it clicks for strings, it clicks for lists and everything else too.

The string toolbox: methods

A method is an action you ask a value to perform on itself, written with a dot. Strings have dozens; here are the ones you'll reach for daily:

text = "  Hello World  "
print(text.upper())       # "  HELLO WORLD  "
print(text.lower())       # "  hello world  "
print(text.strip())       # "Hello World" (trims outer spaces)
print(text.replace("World", "Python"))  # "  Hello Python  "
print("Hello World".split())  # ['Hello', 'World'] -> a list of words

An important subtlety: these methods do not change the original string. Strings in Python are immutable — they can never be modified in place. Every method hands you back a brand-new string. So you must capture the result:

name = "mehul"
name.upper()           # this result is thrown away!
print(name)            # still "mehul"

name = name.upper()    # capture it back into the variable
print(name)            # "MEHUL"

Searching and checking inside text

You'll constantly ask questions about text. Python makes them read like English:

email = "student@codaiman.com"
print("@" in email)              # True — is @ present?
print(email.startswith("std"))   # False
print(email.endswith(".com"))    # True
print(email.find("@"))           # 7 — the index where @ sits
print(len(email))                # 20 — how many characters

The in keyword is wonderfully readable and works everywhere in Python. len() gives the length of almost anything — strings, lists, and more — so it's worth remembering early.

Putting it together: a tiny validator

Let's combine these tools into something useful — a check that a typed email looks roughly valid:

email = input("Enter your email: ").strip().lower()

has_at = "@" in email
has_dot = "." in email
long_enough = len(email) >= 5

if has_at and has_dot and long_enough:
    print(f"Thanks! We'll contact you at {email}")
else:
    print("That doesn't look like a valid email.")

Look how readable that is. We trim and lowercase the input in one chained line, ask three plain-English questions, and combine them with and. This is the real flavour of Python: small, clear pieces that snap together. We used an if statement there to make a decision — and decisions are exactly what the next chapter is about.