ValueError: need more than 0 values to unpack

Question

I am new to python and I am trying make a program that reads a file, and puts the information in its own vectors. the file is an xyz file that looks like this:

45 

Fe -0.055 0.033 -0.047
N -0.012 -1.496 1.451
N 0.015 -1.462 -1.372
N 0.000 1.386 1.481
N 0.070 1.417 -1.339
C -0.096 -1.304 2.825
C 0.028 -1.241 -2.739
C -0.066 -2.872 1.251
C -0.0159 -2.838 -1.205

Starting from the 3rd line I need to place each in its own vectors, so far I have this:

file=open("Question4.xyz","r+")
A = []
B = []
C = []
D = []
counter=0
for line in file:
    if counter>2: #information on particles start on the 2nd line
        a,b,c,d=line.split()
        A.append(a)
        B.append(float(b))
        C.append(float(c))
        D.append(float(d))
    counter=counter+1

I am getting this error:

 File "<pyshell#72>", line 3, in <module>
    a,b,c,d=line.split()
ValueError: need more than 0 values to unpack

Any ideas on where I am going wrong?

Thanks in advance!

Solution

It looks like you have lines in your that doesn't actually result in 4 items on splitting. Add a condition for that.

for line in file:
    spl = line.strip().split()
    if len(spl) == 4:  # this will take care of both empty lines and 
                       # lines containing greater than or less than four items
        a, b, c, d = spl
        A.append(a)
        B.append(float(b))
        C.append(float(c))
        D.append(float(d))

Comments

[Ashwini Chaudhary]

this will fail for the first line containing '45'.

[scrayon]

Thanks - those extra additions will help

[Pierre GM]

@AshwiniChaudhary This won't, as counter = 0 in that case.

[Pierre GM]

And... what if len(spl) != 4? Your just skipping the line, without knowing it. Better let your code whine.

[Ashwini Chaudhary]

then you can add anything in the else part, handle that line in else part.

[RICHA AGGARWAL]

return type of function does not match with values expected in function... check the number of variables returned from function and variables you are expecting