Outline for October 14, 2024

Reading: text, §6.1–6.8
Due: Homework 1, due October 14, 2024

1. Sequences
   1. Sequences are a series of values in a particular order
   2. In Python predominantly strings and lists but also sets and tuples

2. Strings
   1. Sequence of characters (characters are strings of length 1)
   2. Strings are immutable; really important for functions

3. Basic string operations
   1. +, concatenation for strings
   2. *, repetition repeats given value
   3. len() returns length of sequence
   4. s in str returns True if s is a substring of str, False otherwise

4. Indexing, var[position]
   1. Count from 0 to len(var)−1
   2. Position can be a negative number to count from right

5. Assignment with indexing doesn’t work as strings immutable x = "hEllo"; x[1] = "e" produces an error

6. Slicing, var[start:end]
   1. Value at index end not included in slice
   2. If omitted, starting value defaults to 0 and ending value defaults to last index + 1
   3. Can use negative index

7. Looping over strings: for i in str

8. Example program [strstuff.py]

9. What you can do with lists
   1. Check membership: in, not in
   2. +: concatenation
   3. *: repetition
   4. list[a:b]: slice list from a to b−1
   5. del list[i]: delete element list[i]; i can be a slice

10. Objects, references, aliasing
    1. For strings, one copy: assume a = "banana"
       1. After b = a or b = a[:], then a is b is True
    2. For lists, multiple copies: assume A = [ 1, 2, 3 ]
       1. After B = A then A is B is True
       2. After B = A[:], then A is B is False

11. Example of sets [sets.py]

Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: [email protected]

ECS 235A, Computer and Information Security Version of October 12, 2024 at 9:22PM

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