Strings are Immutable¶

Even though you can manipulate a string to create a new string the original string is immutable which means that it doesn’t change. Notice that after you execute the code below the string stored in the variable sentence hasn’t changed.

While the strings themselves can’t be changed you can change the value of a variable. This throws away the original string and sets the variable’s value to the new string.

csp-4-3-1: Given the following code segment, what is the value of the string s1 after these are executed?

s1 = "xy"
s2 = s1
s1 = s1 + s2 + "z"

xyz
s1 will equal "xy" plus another "xy" then z at the end.
xyxyz
s1 contains the original value, plus itself, plus "z"
xy xy z
No spaces are added during concatenation.
xy z
No spaces are added during concatenation, and an additional "xy" should be included at the beginning.
z
s1 was set to "xy" initially, so the final answer will be "xyxyz"

csp-4-3-2: What is the value of s1 after the following code executes?

s1 = "HEY"
s2 = s1.lower()
s3 = s2.capitalize()

Hey
This would be correct if we had asked what the value of s3 was. What is the value of s1?
hey
This would be true if we asked what the value of s2 was after the code executes. What is the value of s1?
HEY
Strings are immutable, meaning they don't change. Any function that changes a string returns a new string. So s1 never changes unless you set it to a different string.