Python, negative numbers string to float

Question

This is a very simple issue but I am making it needlessly complex and continue to hit road blocks.

I am trying to parse a simple text file which contains point cloud information, x, y, z.

It looks like this:

vertices:
v -543.243 -494.262 1282
v -538.79 -494.262 1282
v -536.422 -496.19 1287
v -531.951 -496.19 1287
v -527.481 -496.19 1287
v -213.909 -223.999 581
v -212.255 -224.384 582
v -209.15 -223.228 579
v -207.855 -223.999 581
v -205.482 -223.613 580
v -203.468 -223.613 580
v -201.106 -223.228 579
v -199.439 -223.613 580
v -197.765 -223.999 581
v -195.41 -223.613 580
v -193.062 -223.228 579
v -190.721 -222.842 578
v -189.04 -223.228 579
v -187.998 -224.384 582
v -185.976 -224.384 582
v -183.955 -224.384 582
v -181.621 -223.999 581
v -179.293 -223.613 580
v -177.279 -223.613 580
v -175.264 -223.613 580
v -173.549 -223.999 581
v -171.531 -223.999 581
v -169.513 -223.999 581
v -167.495 -223.999 581
v -165.761 -224.384 582
v -163.74 -224.384 582
v -161.718 -224.384 582
v -159.697 -224.384 582
v -157.946 -224.77 583
v -155.921 -224.77 583
v -153.896 -224.77 583
v -151.871 -224.77 583
v -149.847 -224.77 583
v -147.568 -224.384 582

Right okay. Not so bad.

Next I am using python in blender to convert these points into vertices:

It looks like so: `

    #Open the file
try:
    f=open(path, 'r')
except:
    print ("Path is not Valid")


#Create an array of 
verts = []
#verts=[float(e) for e in verts if e]
#values = []

for line in f:
    lines = f.readline() 
    #values = ([c for c in lines if c in '-1234567890.'])
    if line.startswith("v "): #Go through file line by line
        read = lines.strip(' v\n').split(',') #remove the v,split@, 
            #read = values.split(',')
        #loop over all stuff in read, remove non-numerics
        for d in read:
            d= d.strip('-').split(' ')
            print("d:", (d))
            for n in d:
                n = n.strip('-')
                verts = verts.append(float(n[0]))
                #verts = verts.append(float(n[2]))
                #verts = verts.append(float(n[3]))
                print("vertsloops", d[0])
            print("read1", read[0])
            print(read)
            print("oo1verts", verts)
             ##################
             #Extend the array# 
             #print ("Could not use the line reading: %s"%read)


# Create a new mesh, it is now empty
mesh = bpy.data.meshes.new("Cube")
# Create empty vertices field in the mesh
mesh.vertices.add(len(verts))
# Add vertices
mesh.vertices.foreach_set("co", verts)


#Add a new empty object named "Read the PointCloud Data"
obj = bpy.data.objects.new("Read the PointCloud Data", mesh)
# Link object to current scene
bpy.context.scene.objects.link(obj)
`

Somehow, I have tried many different combinations of splitting the string, but still getting errors. I know this is a simple task!?! Any Advice please!

The errors I get look at first like:

d: ['-536.422', '-496.19', '1287']
Traceback (most recent call last):
  File "/Users/.../importpoints.blend/importpoints", line 37, in <module>
ValueError: could not convert string to float: '-'
Error: Python script fail, look in the console for now...

And Then like so :

d: ['536.422', '-496.19', '1287']
vertsloops 536.422
Traceback (most recent call last):
  File "/Users/.../importpoints.blend/importpoints", line 37, in <module>
AttributeError: 'NoneType' object has no attribute 'append'
Error: Python script fail, look in the console for now...

One thing is, how come float('-531') won't be handled as a negative number. As it stands, it hits the '-' sting and considers it non-numeric so it cannot convert it. But its negative, so how can I indicate that???

Thanks.

Answer 1

Make your reading a bit shorter:

verts = []
for line in f:
    if line.startswith('v '):
        verts.append([float(val) for val in line.split()[1:]])

This should replace your full for line in f: loop. Make sure there is no other line later starting with v in your file. Maybe there is an empty line after the values, so you can stop reading there.

Now verts looks like this:

[[-543.243, -494.262, 1282.0],
 [-538.79, -494.262, 1282.0],
 [-536.422, -496.19, 1287.0],
 [-531.951, -496.19, 1287.0],
 [-527.481, -496.19, 1287.0],
 [-213.909, -223.999, 581.0],
 [-212.255, -224.384, 582.0],
 [-209.15, -223.228, 579.0],
 [-207.855, -223.999, 581.0],
 [-205.482, -223.613, 580.0],
 [-203.468, -223.613, 580.0],
 [-201.106, -223.228, 579.0],
 [-199.439, -223.613, 580.0],
 [-197.765, -223.999, 581.0],
 [-195.41, -223.613, 580.0],
 [-193.062, -223.228, 579.0],
 [-190.721, -222.842, 578.0],
 [-189.04, -223.228, 579.0],
 [-187.998, -224.384, 582.0],
 [-185.976, -224.384, 582.0],
 [-183.955, -224.384, 582.0],
 [-181.621, -223.999, 581.0],
 [-179.293, -223.613, 580.0],
 [-177.279, -223.613, 580.0],
 [-175.264, -223.613, 580.0],
 [-173.549, -223.999, 581.0],
 [-171.531, -223.999, 581.0],
 [-169.513, -223.999, 581.0],
 [-167.495, -223.999, 581.0],
 [-165.761, -224.384, 582.0],
 [-163.74, -224.384, 582.0],
 [-161.718, -224.384, 582.0],
 [-159.697, -224.384, 582.0],
 [-157.946, -224.77, 583.0],
 [-155.921, -224.77, 583.0],
 [-153.896, -224.77, 583.0],
 [-151.871, -224.77, 583.0],
 [-149.847, -224.77, 583.0],
 [-147.568, -224.384, 582.0]]

Answer 2

There's no problem converting to float a string of a negative number

>>> float('-5.6')
-5.6
>>> float('-531')
-531.0

Here's an example to parse a single line

>>> line = 'v -543.243 -494.262 1282'
>>> line.split()
['v', '-543.243', '-494.262', '1282']
>>> v, x, y, z = line.split()
>>> x 
'-543.243'
>>> y
'-494.262'
>>> z
'1282'

Now we convert:

>>> x = float(x)
>>> x
-543.243

Answer 3

Thanks all, that helped a lot. Below is the final code if anyone needs it.

#path='Insert Path here' 

path='/OBJS2015-12-04-20-26-38-532.txt'

print('hello world')
######################################################################################

#Open the file
try:
    f=open(path, 'r')
except:
    print ("Path is not Valid")


#Create an array of vertices

vertices = []
#vee = []
t = ()
for line in f:
    if line.startswith('v '):
        vee = [float(val) for val in line.split()[1:]]
        t = tuple(vee)
        vertices.append(t)


#Define vertices, faces, edges
verts = vertices
faces = []


#Define mesh and object
mesh = bpy.data.meshes.new("Cube")
object = bpy.data.objects.new("Cube", mesh)

#Set location and scene of object
object.location = bpy.context.scene.cursor_location
bpy.context.scene.objects.link(object)

#Create mesh
mesh.from_pydata(verts,[],faces)
mesh.update(calc_edges=True)

Answer 4

So just to add to the answers...

First off, you should exit the program in the Except clause cause it'll continue and raise a value error cause f wont be defined.

except:
    print "Invalid Path"
    exit() #Or some other way to exit

and second, assuming you correctly opened the file in read mode, shouldn't you do lines.split ('\n') to get each different line?

lines = lines.split('\n') ##Creates a list of new-lines

Again, just adding to the answers... Hopefully that helped a little!

Answer 5

For others, coming across this thread. This is also due to the usage of non-ASCII characters to represent "-". Simply fix the non-ascii character in the float representation using regex or other methods and the conversion would work. More details available at Python convert string to float error with negative numbers