CODEWITHSUNDEEP
pythonpython-2.7
Adam Burros
Adam Burros

Reputation: 121

Python appending not working as expected

x_list = [0, 0]
y_list = [0, 1]
def coordinates(condition_x, condition_y):
    zipped = zip(x_list, y_list)
    condition_coord = condition_x,condition_y
    for a,b in zipped:
        print a,b
        coord = a,b
        if condition_coord != coord:
            x_list.append(condition_x)
            y_list.append(condition_y)
        else:
            print "Already a room there"

print x_list
print y_list    
coordinates(0,1)
print x_list
print y_list

For this code what I'm trying to accomplish is this: There are two lists x_list and y_list, and I'm checking to see if there are any coordinate pairs already there. The first index of x_list and y_list is the first coordinate, the second index of both of them is the second coordinate, etc.

In the coordinates function I want to look at both of the lists, and test to see if that coordinate is already present, and if not it appends it to the 2 lists, creating another coordinate pair.

The error that I'm getting is when it's tested, it says both "Already a room there" and appends the coordinates to the list, even though they're already there.

Example:

coordindates(0,1)
coordindates(0,2)

is supposed to return "Already a room there" for the first call, and appends 0 to X_list and 2 to y_list for the second.

Upvotes: 1

Views: 95

Answers (4)

Andriy Ivaneyko
Andriy Ivaneyko

Reputation: 22031

Your code shall be modified to update coordinates after performing for loop over zipped x_list, y_list, below is modified for loop with comments:

match = False
for a,b in zipped:
        print a,b
        coord = a,b
        if condition_coord == coord: # coord matched
           match = True # set match flag and break for loop, no reason to continue
           break

if not match: # if match Falsy we have to update x_list and y_list
    x_list.append(condition_x)
    y_list.append(condition_y)
else:
    print "Already a room there"

Or alternative version of coordinates method:

def coordinates(cond_x, cond_y):
    if (cond_x, cond_y) not in zip(x_list, y_list):
        x_list.append(cond_x)
        y_list.append(cond_y)
    else:
        print "Already there"

Upvotes: 0

Moses Koledoye
Moses Koledoye

Reputation: 78556

You should use a better test condition. As is, your condition adds a new coordinate when at least one test passes, instead, it should add when all the coordinates pass the test. You should use all:

x_list = [0, 0]
y_list = [0, 1]

def coordinates(condition_x, condition_y):
    zipped = zip(x_list, y_list)
    condition_coord = condition_x,condition_y
    #if all((a, b) != condition_coord for a, b in zipped):
    if condition_coord not in zipped:
        x_list.append(condition_x)
        y_list.append(condition_y)
    else:
        print "Already a room there"

Upvotes: 0

Marco Sulla
Marco Sulla

Reputation: 15930

You're code can't work, since you do the check-and-add for every couple. So if you have N coordinates, you'll add the new coordinate N times, or N-1 if it's already present. You have to do something like this:

def coordinates(condition_x, condition_y):
    zipped = zip(x_list, y_list)
    condition_coord = condition_x,condition_y
    in_lists = False

    for a,b in zipped:
        print a,b
        coord = a,b
        if condition_coord = coord:
            in_lists = True
            break

    if not in_lists:
        x_list.append(condition_x)
        y_list.append(condition_y)

or better, just use a set of tuples:

>>> coordinates = {(5, 7), (9, 0), (0, 1)}
>>> coordinates
set([(0, 1), (9, 0), (5, 7)])
>>> coordinates.add((5, 7))
>>> coordinates
set([(0, 1), (9, 0), (5, 7)])
>>> coordinates.add((4, 4))
>>> coordinates
set([(0, 1), (9, 0), (5, 7), (4, 4)])

Upvotes: 1

brodie
brodie

Reputation: 61

The problem is that you are just checking if one coordinate does not match your condition coord. You could still search through but a better way is to harness Python's in:

x_list = [0, 0]
y_list = [0, 1]

def coordinates(condition_x, condition_y):
    if (condition_x, condition_y) not in zip(x_list, y_list):
        x_list.append(condition_x)
        y_list.append(condition_y)
    else:
        print 'Already a room there'

print x_list
print y_list    
coordinates(0, 1)
print x_list
print y_list

Still better is to use a set.

Upvotes: 1

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