Most of the data you will ever handle is text: names, addresses, log lines, JSON, HTML. Python’s string type is good enough that people pick the language for this reason alone.
Quotes
Single and double quotes do the same thing. Use whichever avoids escaping:
print('single')
print("double")
print("She said 'hello'")
print('It costs $5 - and that is "cheap"')
# Triple quotes span lines and keep the line breaks.
print("""Dear Ada,
Thank you for the algorithm.""")f-strings
To put a value inside text, prefix the string with f and write the
expression in braces. This is the modern way to format in Python, and the only
one you need.
name = "Ada"
age = 36
print(f"{name} is {age} years old")
# Any expression fits inside the braces.
print(f"Next year {name} turns {age + 1}")
# :.2f rounds to 2 decimals, :, adds thousands separators.
price = 1234.5678
print(f"Price: {price:.2f}")
print(f"Big: {1234567:,}")
# = is a debugging trick: it prints the expression and its value.
print(f"{age * 2 = }")Format specifiers worth remembering
:.2f fixed decimals · :, thousands separators · :>10 right-align in 10
columns · :<10 left-align · :^10 centre · :.1% percentage.
Strings are sequences
A string is an ordered sequence of characters, and positions count from zero.
word = "Python"
print(word[0]) # first character
print(word[5]) # sixth
print(word[-1]) # last - negative counts from the end
print(len(word)) # how many characters
# Slicing takes [start:stop] - stop is not included.
print(word[0:3])
print(word[:3]) # from the beginning
print(word[3:]) # to the end
print(word[::-1]) # every character, backwardsThe half-open rule — start included, stop excluded — looks odd for about a
day and then becomes convenient: word[:3] and word[3:] split cleanly with
no overlap and no gap.
Useful methods
A method is a function that belongs to a value; you call it with a dot. Strings have dozens, and these are the ones that earn their keep:
raw = " Ada Lovelace,Programmer "
print(raw.strip()) # remove surrounding whitespace
print(raw.strip().upper())
print(raw.strip().lower())
print(raw.replace(",", " - "))
print(raw.strip().split(",")) # cut into a list on a separator
print("ada" in raw.lower()) # substring test
print(raw.strip().startswith("Ada"))
print("-".join(["2026", "01", "05"]))Strings never change
Every method above returns a new string; none of them edits the original.
raw.strip() on its own line does nothing useful — you have to keep the
result: raw = raw.strip(). This is called immutability, and it is why strings
are safe to share around a program.
name = "ada"
name.upper() # result thrown away
print(name)
name = name.upper() # result kept
print(name)Escape sequences
Some characters need a backslash to write: \n is a newline, \t a tab, \"
a literal quote, \\ a literal backslash.
print("Line one\nLine two")
print("Name:\tAda")
print("A backslash: \\")
# A raw string turns escapes off - handy for Windows paths and regexes.
print(r"C:\new\table")Before you write your own
Predict. Four lines. Decide each one before you press Run.
word = "spending"
print(word[0], word[-1])
print(word[:5])
print(f"{len(word)} letters")
answer = " Yes "
print("yes" in answer.lower())Check your prediction
s g
spend
8 letters
Trueword[:5] stops before position 5, so it’s the first five characters:
s p e n d. And answer.lower() is " yes ", which contains "yes" —
the spaces don’t matter to in.
Fix. A survey answer should come out tidy as [blue] — the brackets are
there so you can see any stray spaces. It comes out unchanged. Why?
answer = " BLue "
answer.strip()
answer.lower()
print(f"[{answer}]")Check your fix
answer = " BLue "
answer = answer.strip().lower()
print(f"[{answer}]")[blue]strip() and lower() each return a new string, and the original lines threw
those new strings away. Keep the result by assigning it back — and you can
chain the two methods, because strip() returns a string that has a
lower() of its own.
Clean up a messy record
The variable below holds a badly formatted record. Print it as:
ADA LOVELACE (programmer) - 36You will need strip, split, upper, lower and an f-string.
record = " ada lovelace | Programmer | 36 "
# Your code hereHint 1: the idea
Separate, then tidy. split("|") cuts the record into three pieces, but each
piece still has spaces around it. Strip each piece, change its case, and put the
three back together with an f-string.
Hint 2: a first step
Start with parts = record.split("|") and print(parts). Look closely at what
you get: the spaces are still there, which tells you what to do to each piece
next. parts[0] is the name.
Show one solution
record = " ada lovelace | Programmer | 36 "
parts = record.strip().split("|")
name = parts[0].strip().upper()
role = parts[1].strip().lower()
age = parts[2].strip()
print(f"{name} ({role}) - {age}")Splitting first and stripping each piece afterwards is the usual shape for this kind of cleanup: separate, then tidy.
What you learned
- Quotes are interchangeable; triple quotes span lines.
- f-strings interpolate any expression, with format specifiers like
:.2f. - Strings are zero-indexed sequences; slices are half-open, negatives count back.
- Methods like
strip,split,replaceandjoinreturn new strings. - Strings are immutable — keep the result or nothing happened.