Lists as Arrays

Python does not have an intrinsic array Type, however, Python does have a list type.

Lists can be used to construct an array structure in Python.

It is the programmer's responsibility when implementing an array structure in Python, to follow the restrictions that arrays have in other programming languages.

In mathematics, an array is called a matrix.

1D Array Examples

1D Example #1

#create an empty list

my_List = []

#print the list

print (my_List)

# create a new element in the list

my_List.append("Hello")

#print the list to see the changes

print (my_List)

# add more elements to the list

my_List.append("how")

my_List.append("are")

my_List.append("you")

#print the list to see the changes

print (my_List)

# change the value of each element

my_List[0]="Good-bye"

my_List[1]="see"

my_List[2]="you"

my_List[3]="later"

#print the list to see the changes

print (my_List)

# other list functions

print (len(my_List))

1D Example#2:

#create an list and fill it with zeros

# Method #1

wordlength = []

for r in range(10):

wordlength.append(0)

print (wordlength)

#create an list and fill it with zeros

# Method #2

wordlength=[0 for x in range(11)]

print(wordlength)

""" count the number of each word with length n """ #create an list and fill it with zeros wordlength=[0 for x in range(11)] # a list of words is required for this example, so make one my_List = [] my_List.append("Good-bye") my_List.append("see") my_List.append("you") my_List.append("later") # for each word in the list, increase the corresponding wordlenth element by one for word in my_List: wordlength[len(word)]+= 1 # neatly print the results print( "length "+"Number Of Words") # why does the range start a 1 and not 0 for i in range(1,len(wordlength)): print (" "*3+str(i)+" "*17+str(wordlength[i]) )

2D Array Examples:

2D Example #1

# create an empty list (array)

u=[]

print("the empty list")

print (u)

#fill the list (array) with no value (None)

for row in range(10):

# create a new empty row

u.append([])

for col in range (5):

#add a new element to the row

u[row].append(None)

# prints the entire list on one line

print("the 2D list")

print (u)

# place a value in a specific element

# values need not be the same type

u[3][2]="hello"

u[0][1]= 7

# prints each row on a line

print("the 2D list: one row at a time")

for row in range(10):

print(u[row])

# prints each element on a line

print("the 2D list: one element at a time")

for row in range(10):

for col in range(5):

print(u[row][col])

# print a specific element

print (u[0][1])

2D Example #2

#create a 2D list (array) and fill it with zeros

table= [ [ 0 for col in range(3) ] for row in range(6) ]

# print the 2D list on one line

print (table)

# add values to each element in the 2D list

for row in range(6):

for col in range(3):

table[row][col]= row*10+col

# print each row on one line

for row in range (6):

print (table[row])

# print the number of rows

print (len(table))

#print the number of cols in row #1

print(len(table[1]))