Strings in depth: slicing, methods and f-strings

 K  e  n  y  a
 0  1  2  3  4
-5 -4 -3 -2 -1

word = "Kenya"
print(word[0], word[-1])      # K a
print(word[1:4])              # "eny"  (from 1 up to, not including, 4)
print(word[:3], word[2:])     # "Ken" "nya"
print(word[::-1])             # "ayneK" reversed
print(len(word))              # 5

phone = "0712345678"
print("Last 4 digits:", phone[-4:])
print("Masked:", phone[:4] + "***" + phone[-3:])

raw = "  mama NJERI's bakery  "
print(raw.strip())                 # remove spaces at both ends
print(raw.strip().title())         # "Mama Njeri'S Bakery" (title case)
print(raw.upper(), raw.lower())
print("0712 345 678".replace(" ", ""))
print("nairobi,mombasa,kisumu".split(","))
print(" - ".join(["Nyeri", "Meru", "Embu"]))
print("Nairobi".startswith("Nai"), "photo.jpg".endswith(".jpg"))
print("banana".count("a"), "banana".find("n"), "banana".find("x"))
print("2026".isdigit(), "abc".isalpha(), "   ".isspace())
print("7".zfill(3), "Hi".center(10, "*"))

name = "Achieng"
amount = 12500.5
items = 3

print(f"Hello {name}!")
print(f"{items} items cost KSh {amount:,.2f}")     # 12,500.50
print(f"{'Item':<10}{'Price':>10}")                 # align left / right
print(f"{'Sugar':<10}{160:>10}")
print(f"{'Oil':<10}{350:>10}")
print(f"Paid: {0.875:.0%}")                         # 88%
print(f"{name=}")                                   # shows name='Achieng' (debugging)
print(f"Next year you'll pay {amount * 1.1:,.0f}")  # maths inside

print("Line one\nLine two")      # \n new line
print("Name:\tAmina")            # \t tab
print("She said \"karibu\"")     # \" a quote inside quotes
print('It\'s fine')
print(r"C:\new\folder")          # raw string: backslashes stay as they are

message = """This is a
multi-line string,
great for SMS templates."""
print(message)

sms = "Your M-Pesa balance is Ksh1,250.00"
digits = ""
for ch in sms:
    if ch.isdigit():
        digits += ch
print(digits)                    # 125000

vowels = sum(1 for ch in "Harambee" if ch.lower() in "aeiou")
print("Vowels:", vowels)

def clean_phone(text):
    digits = "".join(ch for ch in text if ch.isdigit())
    if digits.startswith("254") and len(digits) == 12:
        digits = "0" + digits[3:]
    if len(digits) == 10 and digits[:2] in ("07", "01"):
        return digits
    return None

for p in ["0712 345 678", "+254 712-345-678", "12345", "0110 123 456"]:
    print(f"{p:<20} -> {clean_phone(p)}")

town = "nairobi"
# town[0] = "N"          # TypeError: 'str' object does not support item assignment
town = "N" + town[1:]     # build a new string
print(town)
print("nairobi".capitalize(), "NAIROBI".lower(), "nairobi city".title())

message = "Confirmed. KSh1,500.00 sent to JOHN KAMAU 0712345678 on 15/9/26"
print("sent" in message)                         # membership
print(message.find("KSh"), message.find("USD"))  # index, or -1 if missing
print(message.count("0"))
print(message.startswith("Confirmed"), message.endswith("26"))
print("0712345678".isdigit(), "Kamau".isalpha(), "ADM001".isalnum())

message = "Confirmed. KSh1,500.00 sent to JOHN KAMAU 0712345678 on 15/9/26"
start = message.find("KSh") + 3
end = message.find(" ", start)
amount = float(message[start:end].replace(",", ""))
phone = [word for word in message.split() if word.isdigit() and len(word) == 10][0]
print("Amount:", amount, "Phone:", phone)

import re
message = "Confirmed. KSh1,500.00 sent to JOHN KAMAU 0712345678 on 15/9/26"
match = re.search(r"KSh([\d,]+\.\d{2})", message)
print(match.group(1) if match else "no amount")
print(re.findall(r"\b0\d{9}\b", "Call 0712345678 or 0722000111"))

items = [("Unga 2kg", 195), ("Sugar 1kg", 180), ("Cooking oil 1L", 380)]
print(f"{'Item':<16}{'Price':>8}")
print("-" * 24)
for name, price in items:
    print(f"{name:<16}{price:>8,.2f}")
print("-" * 24)
print(f"{'Total':<16}{sum(p for _, p in items):>8,.2f}")
print(", ".join(name for name, _ in items))