String Methods

A string is more than just a piece of text we display. Python offers us many tools to inspect and modify strings, and we’re going to look at the most useful ones

How long is a name? How many letters does it have? len() tells us

name = "Tommy Vercetti"
print(len(name))

Output 14. Yes, the space counts too. Every character matters, including commas, dots, exclamation marks, and any other character. Try with len("password-!@#

We can transform a string to uppercase or lowercase

name = "tommy vercetti"
print(name.upper())   # TOMMY VERCETTI
print(name.lower())   # tommy vercetti

Notice the dot between name and upper(). The dot syntax means: "take this string and apply this method to it". A method is just a function that belongs to something, in this case to a string

Important: name.upper() does NOT change the original variable. It returns a new string

name = "tommy vercetti"
name.upper()
print(name)

Will print tommy vercetti, lowercase as before, because we did nothing with the result of name.upper(). To actually keep it uppercase

name = "tommy vercetti"
name = name.upper()
print(name)

Now name stores the new value. This kind of trap catches absolutely everyone in the beginning. If we read from top to bottom, the story is simple: we have a name, then we turn it uppercase and update the name, then we print it

We can glue strings together with +. This is called concatenation

first_name = "Tommy"
last_name = "Vercetti"
full_name = first_name + last_name
print(full_name)

Output TommyVercetti. If we want a space between the first name and the last name, we have to concatenate it too

first_name = "Tommy"
last_name = "Vercetti"
full_name = first_name + " " + last_name
print(full_name)

We can grab a piece of a string by giving its start and end position

name = "Tommy Vercetti"
print(name[0])      # T
print(name[1])      # o
print(name[0:5])    # Tommy
print(name[6:14])   # Vercetti

name is a variable - we already know that. Why is name[0] = T? Why is name[1] = o? In fact, why does name[something] = something else?

Let's imagine the variable name as a row of little boxes, each box holding a single character. Under each box is written its position number

Tommy Vercetti
^ 0 1:green

In programming, counting starts from 0, NOT from 1. So name[0] is the first letter (the box at position 0, highlighted above), name[1] is the second, and so on. When we write name[something], something is the position number, and Python gives us the character in that box. For example, name[9] means "give me the character at position 9 in name", which is the character c

name[0:5] means "from position 0, up to but NOT including position 5". So we take positions 0, 1, 2, 3, 4, which spell Tommy. Just like with range() in the for loop, the end is exclusive (we don’t take it)

We can also leave one of the numbers out

name = "Tommy Vercetti"
print(name[:5])    # Tommy   (from start to 5 - 1)
print(name[6:])    # Vercetti (from 6 to the end)

Mission: Position Decoder

The station reads only certain positions from a code word. The program reads a word into a variable and prints, on separate lines:

• the character at position 0
• the character at position 3
• the first 4 characters
• the characters from position 4 to the end

Example

If the user types

Andromeda

the program should print

A
r
Andr
omeda