Computer Programming 150

(April 9, 2008)

Coding for List Methods

1. <list>.append(x): appends x to end of list

list + [x]

2. <list>.sort()

def minIndex(n , list):

#

# returns index of smallest value in the slice list[n:]

#

currMinIndex = n

for i in range(n+1, len(list)):

if (list[i] < list[currMinIndex]):

currMinIndex = i

return currMinIndex

def selectionSort(list):

#

# selection sort - returns list in ascending order

#

for n in range(len(list)-1):

k = minIndex(n, list) # get index of smallest element in list[n:]

list[k], list[n] = list[n], list[k] # swap with list[n]

print n, k, list # trace

return list

3. <list>..reverse()

def reverse(list):

#

# reverses items in list

#

n = len(list)

for i in range(n/2): # half the list

list[i], list[n-1-i] = list[n-1-i], list[i] # swap items

4. <list>.index(x): returns index of x in list

def index(x, list):

#

# returns location of value x in list

# if not found returns length of list

#

i = 0;

while (i < len(list) and x != list[i]): # “standard” search loop

i = i + 1

return i

5. <list>.insert(i, x) : inserts x into list at location i

def insert(i, x, list):

#

# inserts x at location i

#

list = list + [0] # add zero to end

n = len(list)-1

while (n > i): # shift values to right

list[n] = list[n-1]

n = n - 1

list[i] = x # insert x in open slot

return list

6. <list>.count(x): counts number of occurrences of x in list

def count(x, list):

#

# counts occurrences of x in list

#

cnt = 0;

for i in list:

if (i == x):

cnt = cnt + 1

return cnt

7. <list>.remove(x): moves item x from list

def remove(x, list):

#

# deletes first occurrence of x in list

#

i = 0

while (i < len(list) and x != list[i]): # “standard” search loop

i = i + 1

return list[:i] + list[i+1:] # concatenate slices where i is position of x

8. <list>.pop(i): removes and returns item at location i

def pop(i, list):

#

# deletes and returns ith component of list

#

x = list[i]

list = list[:i] + list[i+1:] # concatenates slices

return x, list