python programming

[scorpious]

I posted this question in absolute beginner talk but should probably have posted it here.

anyway here's my programme



def start():
size = (raw_input("Board size: "))
number = ['2','3','4','5','6','7','8','9']
while size not in number:
print 'must be between 2 and 9'
size = (raw_input("Board size: "))
size = int(size)
return size


def set_up(n):
row = []
grid = []
count = 0
while count != n:
row.append('.')
count += 1
count = 0
while count != n:
grid.append(row)
count += 1
return grid

def assign_numbers(grid):
print grid
list = grid
count = 0
number = len(list) - 2
start = 3
while count <= number:
list [count][0] = start
print list
count += 1
start = start - 1
return list

def assign_letters(grid):
print grid
new_list = grid[-1]
number = len(new_list)
letters = ['.','a','b','c','d','e','f','g','h']
letters = letters[0:number]
grid[-1] = letters
print grid




grid_size = start()
grid1 = set_up(grid_size)
grid2 = assign_numbers(grid1)
grid3 = assign_letters(grid2)
print grid3when I input '4' I expected it to print

[['3', '.', '.', '.'], ['2', '.', '.', '.'], ['1', '.', '.', '.'], ['.', 'a', 'b', 'c']]but the assign_numbers function is giving me grief and i get

[['1', '.', '.', '.'], ['1', '.', '.', '.'], ['1', '.', '.', '.'], ['.', 'a', 'b', 'c']]can anyone tell me why it returns a whole bunch on 1s?

cheers
Tom

[Tony Flury]

it is due to the way that python applies objects and creates lists.

When you append row to grid - in your set_up function - you get n references to the same row object - so when you change grid[0] - you change the row object.

you need something like :



grid.append(list(row))


To ensure you get a copy of your empty row - and not a copy of the reference.

http://docs.python.org/library/functions.html?highlight=function%20list#list

[lavinog]

Try this:

def set_up(n):
row = []
grid = []
count = 0
while count != n:
row.append('.')
count += 1
count = 0
while count != n:
grid.append(row[:])
count += 1
return grid


row[:] will make a copy of row instead of linking the same list object.

[scorpious]

It works! You two are geniuses!

Thank you so much!!!




Lots of frustration right there haha :)

[lavinog]

I made some changes to the code to demonstrate some other ways you can accomplish those tasks:



def start():
size = (raw_input("Board size: "))
number = ['2','3','4','5','6','7','8','9']
while size not in number:
print 'must be between 2 and 9'
size = (raw_input("Board size: "))
size = int(size)
return size


def set_up(n):
grid = list()
row = ['.'] * n # Creates ['.', '.', '.', '.',...etc]
for r in range(n):
grid.append(row[:])
return grid

def assign_numbers(grid):
list_ = grid # Avoid keywords (like list) for variables

start = 3

for row in list_[:-1]: #list_[:-1] stops before last row
row[0]=start
start-=1 # same as start = start - 1
return list_

def assign_letters(grid):
number = len(grid)
letters = ['.','a','b','c','d','e','f','g','h']
grid[-1] = letters[0:number]
return grid




grid_size = start()
grid1 = set_up(grid_size)
grid2 = assign_numbers(grid1)
grid3 = assign_letters(grid2)
print grid3

[Tony Flury]

Try this:


row[:] will make a copy of row instead of linking the same list object.

Odd - i am sure i tried that - and it did not work - and now it does.