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String Manipulation Techniques

Who this is for:

  • Grade 8–9 students who already know Python basics (variables, input, loops, functions)

Why this matters:

Strings are everywhere: names, chat messages, file paths, and more. Learning to slice, clean, search, and format strings makes your programs easier to read and more powerful.

Goals:

  • Treat strings as sequences (indexing and slicing)
  • Clean and transform text with common string methods
  • Search inside strings and replace parts safely
  • Split and join words
  • Format strings neatly with f-strings
  • Build a small text tool using these skills

Key ideas and examples

1) Strings are sequences

  • You can think of a string as a row of characters, each with a position (index).
  • Indexing starts at 0. Negative indexes count from the end.

Example:

text = "Python" print(text[0]) # 'P' print(text[-1]) # 'n' print(text[1:4]) # 'yth' (from index 1 up to, but not including, 4) print(text[:2]) # 'Py' print(text[2:]) # 'thon' print(text[::-1]) # 'nohtyP' (reversed)

2) Strings are immutable

  • You can't change a string in place. You create new strings instead.

Example:

name = "Sam" # name[0] = "J" # This would cause an error name = "J" + name[1:] print(name) # 'Jam'

3) Concatenation and repetition

  • Use + to join strings and * to repeat.

Example:

greet = "Hi" + " " + "there" echo = "ha" * 3 print(greet) # 'Hi there' print(echo) # 'hahaha'

4) Escaping and multi-line strings

  • Use backslash to escape quotes or special characters. Triple quotes for multi-line.

Example:

quote = "She said, \"Hello!\"" path = "C:\\Users\\You" haiku = """Code flows softly over keys and tiny bugs fixed at break of day""" print(quote) print(path) print(haiku)

5) Change case and trim whitespace

  • .lower(), .upper(), .title()
  • .strip() removes spaces at both ends (or chosen characters), .lstrip(), .rstrip()

Example:

raw = " hello PyVerse! " clean = raw.strip() print(clean) # 'hello PyVerse!' print(clean.upper()) # 'HELLO PYVERSE!' print("mr. bean".title()) # 'Mr. Bean'

6) Find, count, and replace

  • 'in' checks membership
  • .find(x) returns the index or -1
  • .count(x) counts occurrences
  • .replace(old, new[, count]) returns a new string

Example:

txt = "banana bread bandana" print("bread" in txt) # True print(txt.find("band")) # 13 print(txt.count("ana")) # 4 print(txt.replace("ana", "ANA", 2)) # first 2 replacements

7) Starts/ends with

  • Use these to quickly check prefixes/suffixes.

Example:

filename = "report_2025.csv" print(filename.startswith("report_")) # True print(filename.endswith(".csv")) # True

8) Split and join

  • .split() turns a string into a list of words.
  • .join(list) glues a list of strings back into one string.
  • split with no argument handles multiple spaces neatly.

Example:

line = " one two three " words = line.split() # ['one', 'two', 'three'] print(words) joined = "-".join(words) print(joined) # 'one-two-three'

9) Check what characters are inside

  • .isalpha(), .isdigit(), .isalnum(), .isspace()

Example:

code = "X9Y" print(code.isalnum()) # True print("123".isdigit()) # True print("Hi".isalpha()) # True print(" \t".isspace())# True

10) Neat formatting with f-strings

  • f-strings insert variables directly and support simple formatting.

Example:

name = "Leena" score = 9.456 print(f"Hi {name}, your score is {score:.1f}/10") # rounds to 1 decimal

Common mini-patterns

A) Normalize spaces

text = " this has extra spaces " normalized = " ".join(text.split()) print(normalized) # 'this has extra spaces'

B) Safe substring search

msg = "no spoilers please" idx = msg.find("spoilers") if idx != -1: print(f"Found at index {idx}") else: print("Not found")

C) Quick palindrome check (ignoring spaces and case)

s = "Never odd or even" simple = s.replace(" ", "").lower() print(simple == simple[::-1]) # True

Mini Project: Acronym and Hashtag Maker

Goal:

Build a small tool that:

  • Cleans the input phrase
  • Creates an acronym (first letter of each word, uppercase)
  • Builds a hashtag version of the phrase (#TitleCaseWithNoSpaces)

Step-by-step:

  1. Ask the user for a phrase.
  2. Strip leading/trailing spaces and normalize multiple spaces to single spaces.
  3. Create an acronym by taking the first character of each word and making it uppercase.
  4. Create a hashtag that starts with # and uses Title Case with no spaces.

Starter code (fill in the blanks if you want a challenge):

phrase = input("Enter a phrase: ") # 1) Clean: strip and normalize spaces clean = " ".join(phrase.strip().split()) # 2) Acronym: first letters of each word, uppercased words = clean.split() acronym = "".join(w[0] for w in words).upper() # 3) Hashtag: Title Case + no spaces hashtag = "#" + "".join(w.title() for w in words) print(f"Cleaned: {clean}") print(f"Acronym: {acronym}") print(f"Hashtag: {hashtag}")

Sample run:

Enter a phrase: national aeronautics and space administration Cleaned: national aeronautics and space administration Acronym: NASA Hashtag: #NationalAeronauticsAndSpaceAdministration

Challenge ideas (optional):

  • If phrase is empty after cleaning, ask again.
  • Limit hashtag length to 30 characters and add "..." if it's longer.
  • Censor a banned word list by replacing matches with "***" using .replace().

Tips and pitfalls

  • Strings are immutable: methods like replace, strip, lower return a new string. Assign the result to keep the changes.
  • .find returns -1 if not found; don't slice using -1 unless you mean the last character.
  • split() with no arguments is great for messy spacing.
  • When joining, make sure you have a list of strings (not numbers). Convert with str() if needed.

Summary

  • Strings are sequences you can index and slice.
  • Use methods like strip, lower, replace, find, count, split, and join to transform text.
  • f-strings make your output clean and readable.
  • With a few techniques, you can build practical text tools like an acronym and hashtag maker.

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