Strings

Formulas

• len(s) = last index + 1
• s[i] is valid for i from 0 to len(s) - 1

Key words

String

: A sequence of characters in quotes, indexed from zero and unchangeable.

Index

: The position number of a character, starting at zero for the first.

Immutable

: Locked against change, so no character of a string can be replaced in place.

Length

: The count of characters in a string, given by len.

Try it in two minutes

1. Quote the text.
2. Index from zero.
3. Count length.

Formulas

• s[a:b] takes characters from a up to b - 1
• s * n repeats s n times
• x in s is True when x occurs inside s

Key words

Slice

: A range s[a:b] taking characters from a up to b - 1.

Concatenation

: Joining strings with plus into one longer string.

Repetition

: Repeating a string n times with the times operator.

Membership

: Testing with in whether a piece occurs inside a string.

Step

: The skip size in a slice that picks every nth character.

Try it in two minutes

1. Range the slice.
2. Join with plus.
3. Check with in.

Key words

upper and lower

: Methods returning the string in full capitals or full small letters.

split

: The method breaking a string into a list at each separator.

join

: The method merging a list of pieces into one string.

find

: The method locating the first position of a piece, or -1 if absent.

strip

: The method trimming spaces from both ends of a string.

Try it in two minutes

1. Change case?
2. Split or join?
3. Find or count?

Formulas

• s[-1] is the last character of s
• Traverse with: for ch in s

Key words

Traversal

: Visiting each character of a string one by one in a loop.

Palindrome check

: Testing whether a string reads the same forward and backward.

Vowel count

: A loop tally of vowel characters found while traversing.

Code comparison

: Ordering strings by the numeric codes of their characters.

Try it in two minutes

1. Loop characters.
2. Test each.
3. Collect result.