问题描述:

`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.

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)])
```

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`

.

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"
```

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"
```