# How to Think Like a Computer Scientist: The PreTeXt Interactive Edition

## Section9.20Summary

This chapter introduced a lot of new ideas. The following summary may prove helpful in remembering what you learned.

### GlossaryGlossary

indexing ([]).
Access a single character in a string using its position (starting from 0). Example: 'This'[2] evaluates to 'i'.
length function (len).
Returns the number of characters in a string. Example: len('happy') evaluates to 5.
for loop traversal (for).
Traversing a string means accessing each character in the string, one at a time. For example, the following for loop:
for ix in 'Example':
...

executes the body of the loop 7 times with different values of ix each time.
slicing ([:]).
A slice is a substring of a string. Example: 'bananas and cream'[3:6] evaluates to ana (so does 'bananas and cream'[1:4]).
string comparison (>, <, >=, <=, ==, !=).
The six common comparision operators work with strings, evaluating according to lexigraphical order
1
http://en.wikipedia.org/wiki/Lexicographic_order
. Examples: 'apple' < 'banana' evaluates to True. 'Zeta' < 'Appricot' evaluates to False. 'Zebra' <= 'aardvark' evaluates to True because all upper case letters precede lower case letters.
in and not in operator (in, not in).
The in operator tests whether one string is contained inside another string. Examples: 'heck' in "I'll be checking for you." evaluates to True. 'cheese' in "I'll be checking for you." evaluates to False.