1. CSE 231 Lab 6

2. Topics to cover Creating Lists & tuples Lists methods
In-place vs not in-place
Patterns
List comprehension
A Python list is a sequence of objects.
It is a sequence like a string.
It shares characteristics such as indexing & slicing, iteration (for) and membership (in) as well as functions such as len().

3. LISTS and tuples A sequence of objects.
It is a sequence like a string.
It shares characteristics such as indexing & slicing, iteration (for) and membership (in) as well as functions such as len().
Mutable vs Immutable
Strings, ints, floats, tuples are all immutable
Lists are Mutable
Tuples are immutable lists

4. Lists my_list = ["Arthur", "King", "of", "the", "Britons"]

5. Lists – Creating Lists
my_list = [] # start off with nothing in the list
my_list = ['I', 'am', 'Full', 'of', 'stuff']
my_list = list(‘CSE231 Rocks') # using list()
['C', 'S', 'E', '2', '3', '1', ' ', 'R', 'o', 'c', 'k', 's']
mixed_list = [“string”, 1, 42.0, True]
Matrix = [[1, 1], [1,1]]

6. List methods: In-place
my_list.append('A') # takes element arg. & puts to end of list
my_list.pop(3) # takes index arg. & takes it out of list
If no argument is given, it pops out the last element
What does this return?
my_list.sort() # sorts entire list & modifies it in place.
What does the function sorted(my_list) do?
my_list.insert(index, value) # Insert value into position index
my_list.remove(value) # removes the first instance of value
# crashes if the value doesn't exist

7. Lists – What is in-place?
some_list = [] some_list.append(1) print(some_list) >>> [1] # Why didn’t I need to do some_list = some_list.append(1) ?
# Methods (like append) on lists happen IN-PLACE meaning there is no return!

8. Lists – What is in-place?
>>> some_list = [3, 1, 7, 2, 4] >>> some_list = some_list.sort() >>> print(some_list) None # uh oh. What happened to the data???
# You reassigned some_list when sort is done in-place!
# The return of a function that does not return something is what?

9. Lists – What is in-place?
>>> some_list = [3, 1, 7, 2, 4] >>> some_list.sort() >>> print(some_list) [1, 2, 3, 4, 7] # All good again!

10. List methods: NOT-IN-PLACE
‘-’.join(my_list) # joins entire list with a delimiter ‘-’
>>my_list = [‘I’, ’am’, ‘Full’, ‘of’, ‘stuff’]
>>my_string= ‘-’.join(my_list)
>>print(my_string)
I-am-Full-of-stuff

11. Split Method >>my_str='I am in my 231 lab‘
split and also strip methods are your best friends with data parsing
By default it separates strings by whitespaces into a list
Very helpful when given lines of data.
>>my_str='I am in my 231 lab‘
>>my_str.split()
['I', 'am', 'in', 'my', '231', 'lab']
>>my_str.split('m')
['I a', ' in ', 'y 231 lab']

12. Patterns Counter: x = 0 # initialize at zero
x += 1 # increment the counter
Strings:
s = ‘’ # initialize with empty string
s += ch # concatenate characters
Lists:
L = [] # initialize with empty list
L.append(value) # append values to the list

13. List Comprehensions L=[] For i in range(3)
L.append(i**3)
L = [i**3 for i in range(3)]
Other examples
>> L = [i**3 for i in range(10) if i%2 == 0]
>>L = [int(x) for x in line_list]
line = “ ” # original data read from a file
line_list = line.split() #split to get a list of strings, SHOULD CONVERT TO INT NEXT