1. Lists: a new type! LISTS! sets of a thing (e.g., sets of ints)
We've got:
ints
floats
booleans
strings
and now… (drum roll)
LISTS!
sets of a thing (e.g., sets of ints)

2. Creating Lists 
To create a list, put a number of expressions in square brackets:
listvar = [ ] #Empty list with nothing in it.
A list with things in it:
# create a list with some items
listvar1 = [2,10,8,4,17] #list of ints
listvar2 = [“spider leg”,”toe of frog”,”eye of newt”, “bat wing”, “slug butter”, ”snake dandruff”] #list of strings
First list is a list of ints
Second list is a list of strings.
Class 1

3. Lists
Overview 
The list type is a container that holds a number of objects, in a given order.
Lists have an order to them
Like a string, in which the order of the characters matters
Examples of lists:
Sound files: a long list of numbers measuring vibrations in the air
any vibrational measurements
The order of the measurements of vibration is dependent on when they occurred in time.
List of class participants
Measurements of movements (e.g., weather)

4. Lists have indices (like strings):
listvar2 = [“spider leg”,”toe of frog”,”eye of newt”, “bat wing”, “slug butter”,”snake dandruff”] Index listvar1 = [2, 10, 8, 4, 17] Index So to use a particular item in the list: x=listvar2[3] #”bat wing” y=listvar1[1] #10 z=listvar2[0] #”spider leg”

5. Lists: Like strings, we can use: len in
listvar2 = [“spider leg”,”toe of frog”,”eye of newt”, “bat wing”, “slug butter”,”snake dandruff”]
listvar1 = [2, 10, 8, 4, 17]
get the length of a list
len(listvar2) # will give you 6
if “eye of newt" in listvar2:
return(“we can do chemistry!")
else:
return(“Sorry, no chemistry today.”)

6. Lists:
Index:
listvar2 = [“spider leg”,”toe of frog”,”eye of newt”, “bat wing”, “slug butter”,”snake dandruff”]
Slice:
listvar1 = [2, 10, 8, 4, 17]
Slicing:
x = listvar2[3:5] #x now holds [“bat wing”,”slug butter”]
y = listvar1[1:2] #y now holds [10]

7. Lists:Slicing (Like strings)
Index: listvar2 = [“spider leg”,”toe of frog”,”eye of newt”, “bat wing”, “slug butter”,”snake dandruff”] Slice: def f(): return(listvar[0:6]) >>[“spider leg”,”toe of frog”,”eye of newt”, “bat wing”, “slug butter”,”snake dandruff”] def g(): return(listvar2[1:3]) >>[”toe of frog”,”eye of newt”] def h(): return(listvar2[-4:-2]) >>[”eye of newt”,”bat wing”] def i(): return(listvar2[-4:4])

8. Stuff we can do to lists that we can’t do with strings:)
listofstuff = [“ant", “bear", “cat", “dog“,”elephant”,”fox”] # assign by index listofstuff[0] = “aardvark" print(listofstuff) >>>[“aardvark", “bear", “cat", “dog“,”elephant”,”fox”] # assign by slice listofstuff[3:5] = [“dolphin"] >>>[“aardvark", “bear", “cat", “dolphin”,”fox”] # delete an element del listofstuff[2] >>>[“aardvark", “bear", “dolphin”,”fox”] # delete a slice del listofstuff[:2] >>>[ “dolphin”,”fox”]

9. Concatenate(join) lists
list1 = [“skeletons", “zombies ", “witches"]
list2 = [“vampires", “ghouls ", “werewolves"]
list3 = list1 + list2
print(list3)
>>>[“skeletons", “zombies ", “witches“,”vampires", “ghouls ", “werewolves"] Or
list1 +=list2
print(list1)
list1[3]?
list1[0]?
list1[6]?
Classes 2 and 3

10. Note: adding to the end of the list:
list1 = [“skeletons", “zombies ", “witches“,”vampires", “ghouls ", “werewolves"] We CAN do: list1[4] = “ghosts” print(list1) >>> [“skeletons", “zombies ", “witches“,”vampires", “ghosts ", “werewolves"] We CAN’T do: list1[6] = “poltergeists” (why not?)

11. Appending to end of list:
list1 = [“skeletons", “zombies ", “witches“,”vampires", “ghouls ", “werewolves"] We CAN’T do: list1[6] = “poltergeists” Instead: list1.append(“poltergeists”) print(list1) >>[“skeletons", “zombies ", “witches“,”vampires", “ghouls ", “werewolves“, ”poltergeists”] Append adds an element to the end of a list (sets aside more RAM memory) Always to the end! It is a method (function) that belongs to anything that is of the list type Appending doesn’t work with strings (They’re immutable!)

12. List Methods Methods are functions that manipulate lists specifically
lists are objects (object-oriented programming)
Objects have methods (functions) associated with them.
E.g., dog objects might have a walking function
Square objects might have a calc_area function
List objects have functions: e.g.,
Add an element
reverse the list
Sort a list
Etc.

13. Removing an item from the list:
list1=[“skeletons", “zombies ", “witches“,”vampires", “ghouls ", “werewolves“, ”poltergeists”]
list1.remove(“werewolves”)
>>[“skeletons", “zombies ", “witches“,”vampires", “ghouls ",”poltergeists”]
Trying to remove something that isn’t in the list gives you an error:
list1.remove(“ghosts”) #ERROR
So check:
if “vampires” in list1:
list1.remove(“vampires”)
print (list1)
>>>[“skeletons", “zombies ", “witches“, “ghouls ", ”poltergeists”]
remove() ONLY removes the first occurrence of an item in the list:
list2 = [8,2,3,1,5,3,8,4,2,3,5]
list2.remove(2)
print(list2)
>>[8,3,1,5,3,8,4,2,3,5]

14. list1=[“skeletons", “zombies ", “witches“, “ghouls ", ”poltergeists”]
Reversing the order of the list:
list1.reverse()
>>>[‘poltergeist’,’ghouls’,’witches’,’zombies’,’skeletons’]
Sorting the list
list1.sort()
>>>[‘ghouls’,’poltergeists’,’skeletons’,’witches’,’zombies’]
list1.sort(reverse = True)
>>>[‘zombies’,’witches’,’skeletons’,’poltergeists’,’ghouls’]
Class 3

15. Other methods available for lists
count(value) – counts the number of times value occurs in list
list2 = [8,2,3,1,5,3,8,4,2,3,5,3]
x = list2.count(3)
print(x)
>>>4
index(value) – returns index of first occurrence of value
list1=[“skeletons", “zombies ", “witches“, “ghouls ", ”poltergeists”]
y = list1.index(“witches”)
print(y)
>>>2

16. insert(f,value)- inserts value at position f
pop([f]) – returns value at position f and removes value from list. Without f, it pops the last element off the list
list1=[“skeletons", “zombies ", “witches“, “ghouls ", ”poltergeists”]
x=list1.pop()
print(x)
>>”poltergeists”
print (list1)
>> =[“skeletons", “zombies ", “witches“, “ghouls ”]
x=list1.pop(2)
>>”witches”
>> [“skeletons", “zombies ", “ghouls ”]
insert(f,value)- inserts value at position f
list1.insert(1,’dragons”)
print(list1)
>>>[“skeletons", “dragons”, “zombies ", “ghouls ”]

17. def rg(x,y): while len(x) > 0: y. append(x
def rg(x,y): while len(x) > 0: y.append(x.pop()) return(y) print(rg(['witch','ghost','werewolf','vampire'],[]))

18. def ry(x,y): while (len(y)>0): x. append(y
def ry(x,y): while (len(y)>0): x.append(y.pop()) return x print(ry([],['a','n','d','i','h','c','e']))

19. def rf(y,ls): while ls. count(y)>0: if y in ls: z = ls. index(y) ls
def rf(y,ls): while ls.count(y)>0: if y in ls: z = ls.index(y) ls.pop(z) return(ls) x = ['a','m','y','a','a','t','a','h'] print(rf('a',x))

20. def f(x,y): k = True while y < len(x)//2: if (x[y]
def f(x,y): k = True while y < len(x)//2: if (x[y] != x[len(x) - y-1]): k=False y+=1 return (x[y] == x[len(x) - y-1]) and k print(f(“noon",0)) print(f("clue",0))

21. def rz(x,y): ind = 0 while (ind < len(y)): if (y[ind] in x): y[ind]='a' ind+=1 return y print(rz(['b','k','e','s','o'],['c','s','t','k','m','o','r','s','n']))

22. def g(x,y):
while (len(x) > 1):
i = randrange(len(x))
y+=x[i]
x = x[:i]+x[i+1:]
return(y+x)
print(g("computer",""))
#A game comes to mind…

23. def h(x): y = "" k = 0 while k<len(x): y+=(x[k][k]) k+= 1 return(y) ls = ['coffin','creepy','hayride','corpse','ghastly'] print(h(ls))

24. def incx(): x = 1 x = x + 1 return incx() print(x) # What is printed here? def decx(): x = x - 1 decx() print(x) # What is printed here? def squrx(): x = 2 x = x * x squrx()

25. Local Variables Remember the story of how functions work?
Islands that come into existence when they are “called” (made to run)
When they’re done running, a volcano erupts and the function island is destroyed
All parts of the island go away EXCEPT the return value
That means that if a variable comes into existence within the function, it ONLY exists while the function is running.
Unless that variable is returned, it ceases to exist when the function is done running

26. Another example: def incx(x): x = x + 1 return k = 2 incx(k)
print(k) #what do you think is printed?

27. To fix: Global Variables!
x = 3 def incx(): global x x = x + 1 return incx() print(x) def decx(): x = x - 1 decx() def squrx(): x = x * x squrx()
To fix: Global Variables!
Global variables outlast functions
Back to our analogy – global variables are airplanes that fly from function to function
By making a variable global, all functions can use it
If one function changes it, it stays changed for other functions
NOTE: You MUST state you’re using the global variable, or python will assume you want to use a local variable.
If in the code -> you said:
def squrx():
x = x * x
return
squrx()
print(x)
You’d get an error

28. st = "lli" def fun1(): st = "croc" st += "us" print(st) return() fun1() def fun2(): global st st = "po"+st+"wog" fun2() def fun3(): st = "umbre"+st[2:4] + "a" return fun3()

29. for y in range(len(ls)): print(ls[y],end="") print() return
ls = [] def f1(x): global ls ls.append(x) return def f2(x,y): ls.insert(x,y) def f3(): ls.pop() def f4(x): ls.remove(x) def f5(x,y): if (len(ls)>y): ls[y]=x def f6(x,y,z): if (y < z): if z<= len(ls): ls[y:z]=x elif (z < y): if y <= len(ls): ls[z:y]=x
def f7():
global ls
for y in range(len(ls)):
print(ls[y],end="")
print()
return
def main():
f1('s')
f1('b')
f2(1,'u')
f2(0,'l')
f6('yu',3,2)
f3()
f2(3,'b')
f6('aim',1,2)
f4('i')
f2(6,'g')
f5('d',2)
f7()
main()

30. For loop: Another loop type
We use For loops when we know exactly how many times the loop will occur
A subset of while loops
Form:
for variable in [value1, value2,value3…lastvalue]:
calculations
Example:
def f():
for x in [1,2,3,4,5]:
print(x)
return(x)
print(f())

31. More for loops: def f(): for x in [1,3,5,7,9]: print(x) return(x)
print(f())
for x in [2,7,1,9,4]:

32. More for loops: def f(): y = 0 ct = 0
for x in [3.2, 7.1, 8.0, 3.4, 5.1]:
print("including " + str(x))
ct +=1
y = y + x
return(y/ct)
print(f())

33. Loops with strings: def f(y): ct = 0
for x in ["puppy","bunny","puppy","bird","echidna","puppy"]:
if x == y:
ct += 1
return(ct)
print(f("puppy"))

34. More for loops: def f(): for x in [0,1,2,3,4]: print(x) return(x)
print(f())
Shortcut: using range
for x in range(5): # range(5) = [0,1,2,3,4]

35. Same? def whilefunc(y): count = 0 total = 0 while (count < y):
total += count
count += 1
return (total)
print(whilefunc(5))
def forfunc(y):
total = 0
for x in range(y):
total += x
return(total)
print(forfunc(5))

36. More on Range: def f(): for x in range(-3,3):
# from -3 up to but not including 3, e.g., [-3,-2,-1,0,1,2]
print(x)
return(x)
print(f())
for x in range(-3,3,2):
# from -3 up to but not including 3, by increments of 2, e.g., [-3,-1,1]
(Can we make a loop go backwards?)

37. What do these do?
def f(ls): y = 1000 total = 0 for x in ls: total = total + int(x) * int(y) y /=10 return(total) print(f(["2","7","1","9"]))
def f(v):
var1 = ""
for x in range(len(v) - 1,-1,-2):
var1 += v[x]
return(var1)
print(f("kebijrtese"))

38. This one?
def f(): strvar = input("enter a number: ") y = 1 z = 0 var1 = "" for x in range(len(strvar)-1,-1,-1): z += int(strvar[x]) * y y*=10 return(z) print(f())
def f(lv):
x = len(lv)
print(x)
for y in range(0,x):
if "t" in lv[y]:
print(lv[y])
return
listvar = ["ham","am","boat","goat","there","anywhere"]
f(listvar)

39. How about this one?
def f(word): newstr = "" for i in range(1,len(word)+1): newstr += word[-i] return(newstr) wvar = "live" print(f(wvar))

40. What does this do? def f(word): high = len(word) low = 0 newstr = ""
for i in range(10):
position = randrange(low, high)
newstr += word[position]
return(newstr)
wvar = “turkey"
print(f(wvar))

41. What do you get? def f(message): newmessage = "" for x in message:
if x == "g":
newmessage += "l"
else:
newmessage += x
return(newmessage)
mvar = "pogysyggabicaggy"
print("new string: " + f(mvar))

42. def fun4(m): z = "" for s in range(len(m)): for y in range(1,len(m[s]),2): z += m[s][y] return(z) ls = [['d','a','r','c','y'],['d','o','o','r'],['a','n','d']] print(fun4(ls))

43. Lists of Lists – Matrices:
def k(m,n): v = [] for x in range(m): ls = [] for y in range(n): ls.append(0) v.append(ls) return(v) m = k(4,5) #what is this? for x in range(4): print(m[x])

44. Accessing a matrix
First, access which list, and then which value in that list:
E.g.,
def makemat():
mat = [[3,2,1,4],[1,4,2,3],[3,3,3,3]]
print(mat[1][2]) #prints 2
makemat() 3 2 1 4

45. Add 1 to the matrix in a random place?
def p(x,m): i = 0 while (i ==0): #why didn’t I use a for loop here? b = randrange(len(m)) c = randrange(len(m[b])) if m[b][c] != 1: m[b][c] = 1 i= 1 return(m) m = p(7,m)

46. Print out the matrix:
Print out matrix with tabs between each num in each row, e.g.,:
def q(m):
for x in range(len(m)):
for y in range(len(m[x])):
print(m[x][y],end = "\t")
print()
return
q(m)