Importing Mathematica expression to Python correctly

Question

I am trying to import a lengthy expression from Mathematica to Python. I copy-pasted the FortranForm of the Mathematica expression to Python, and set all the lines to have the same indent. But I am getting an error that I don't understand. I am guessing that this is a problem with the indentation, but I am not sure. Please help.

This is the code in Python, with indentation:

def f2(x,y,z,x1,y1,z1,x2,y2,z2,x3,y3,z3):
    return ((x2*(y - y1) + x*(y1 - y2) + x1*(-y + y2))*(y2 - y3) + (-y1 + y2)*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
    (x2*(z - z1) + x*(z1 - z2) + x1*(-z + z2))*(z2 - z3) + (-z1 + z2)*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)))/
    (np.sqrt((x - x1)**2 + (y - y1)**2 + (z - z1)**2)*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)*np.sqrt((x - x3)**2 + (y - y3)**2 + (z - z3)**2)) - 
    ((x - x3)*((x2*(-y + y1) + x1*(y - y2) + x*(-y1 + y2))*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
    (x2*(-z + z1) + x1*(z - z2) + x*(-z1 + z2))*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)) + 
    (y2*(-z + z1) + y1*(z - z2) + y*(-z1 + z2))*(y3*(-z + z2) + y2*(z - z3) + y*(-z2 + z3))))/
    (np.sqrt((x - x1)**2 + (y - y1)**2 + (z - z1)**2)*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)*((x - x3)**2 + (y - y3)**2 + (z - z3)**2)**1.5) - 
    (2*(x - x2)*((x2*(-y + y1) + x1*(y - y2) + x*(-y1 + y2))*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
    (x2*(-z + z1) + x1*(z - z2) + x*(-z1 + z2))*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)) + 
    (y2*(-z + z1) + y1*(z - z2) + y*(-z1 + z2))*(y3*(-z + z2) + y2*(z - z3) + y*(-z2 + z3))))/
    (np.sqrt((x - x1)**2 + (y - y1)**2 + (z - z1)**2)*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)**2*np.sqrt((x - x3)**2 + (y - y3)**2 + (z - z3)**2)) - 
    ((x - x1)*((x2*(-y + y1) + x1*(y - y2) + x*(-y1 + y2))*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
    (x2*(-z + z1) + x1*(z - z2) + x*(-z1 + z2))*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)) + 
    (y2*(-z + z1) + y1*(z - z2) + y*(-z1 + z2))*(y3*(-z + z2) + y2*(z - z3) + y*(-z2 + z3))))/
    (((x - x1)**2 + (y - y1)**2 + (z - z1)**2)**1.5*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)*np.sqrt((x - x3)**2 + (y - y3)**2 + (z - z3)**2))

This is the error that I get:

File "<ipython-input-87-f30bebfee3b2>", line 4
x2*(z - z1) + x*(z1 - z2) + x1*(-z + z2))*(z2 - z3) + (-z1 + z2)*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)))/
SyntaxError: invalid syntax

What is that? Some kind of expansion? Have you checked to see if it's supported by `numpy` / `scipy`? — roganjosh, Jan 04 '17 at 00:36
The code is pretty ugly. Try editing it by looking at [PEP 8](https://www.python.org/dev/peps/pep-0008/#maximum-line-length) — Lucas, Jan 04 '17 at 00:38

score 4 · Accepted Answer · edited May 23 '17 at 11:53

The invalid syntax is the line-break in the expression. E.g.,

def invalid_break():
    return 1 /
           2

is invalid. A simple fix is to wrap the expression in brackets:

def valid_break():
    return (1 / 
            2)

See e.g., How can I do a line break (line continuation) in Python? To be crystal clear, one fix is to wrap your long expression in brackets, i.e.

def f2(x,y,z,x1,y1,z1,x2,y2,z2,x3,y3,z3):
        return (((x2*(y - y1) + x*(y1 - y2) + x1*(-y + y2))*(y2 - y3) + (-y1 + y2)*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
        (x2*(z - z1) + x*(z1 - z2) + x1*(-z + z2))*(z2 - z3) + (-z1 + z2)*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)))/
        (np.sqrt((x - x1)**2 + (y - y1)**2 + (z - z1)**2)*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)*np.sqrt((x - x3)**2 + (y - y3)**2 + (z - z3)**2)) - 
        ((x - x3)*((x2*(-y + y1) + x1*(y - y2) + x*(-y1 + y2))*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
        (x2*(-z + z1) + x1*(z - z2) + x*(-z1 + z2))*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)) + 
        (y2*(-z + z1) + y1*(z - z2) + y*(-z1 + z2))*(y3*(-z + z2) + y2*(z - z3) + y*(-z2 + z3))))/
        (np.sqrt((x - x1)**2 + (y - y1)**2 + (z - z1)**2)*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)*((x - x3)**2 + (y - y3)**2 + (z - z3)**2)**1.5) - 
        (2*(x - x2)*((x2*(-y + y1) + x1*(y - y2) + x*(-y1 + y2))*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
        (x2*(-z + z1) + x1*(z - z2) + x*(-z1 + z2))*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)) + 
        (y2*(-z + z1) + y1*(z - z2) + y*(-z1 + z2))*(y3*(-z + z2) + y2*(z - z3) + y*(-z2 + z3))))/
        (np.sqrt((x - x1)**2 + (y - y1)**2 + (z - z1)**2)*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)**2*np.sqrt((x - x3)**2 + (y - y3)**2 + (z - z3)**2)) - 
        ((x - x1)*((x2*(-y + y1) + x1*(y - y2) + x*(-y1 + y2))*(x3*(-y + y2) + x2*(y - y3) + x*(-y2 + y3)) + 
        (x2*(-z + z1) + x1*(z - z2) + x*(-z1 + z2))*(x3*(-z + z2) + x2*(z - z3) + x*(-z2 + z3)) + 
        (y2*(-z + z1) + y1*(z - z2) + y*(-z1 + z2))*(y3*(-z + z2) + y2*(z - z3) + y*(-z2 + z3))))/
        (((x - x1)**2 + (y - y1)**2 + (z - z1)**2)**1.5*((x - x2)**2 + (y - y2)**2 + (z - z2)**2)*np.sqrt((x - x3)**2 + (y - y3)**2 + (z - z3)**2)))

@roganjosh I realize that `/` is division and `\\`` is explicit line continuation. The syntax error is an invalid line-break in the OP's code, which happens to occur after a division `/` — innisfree, Jan 04 '17 at 00:45
@innisfree So, are you saying that there is an implicit invalid linebreak after the `/` division sign? How do I fix that? By adding parentheses around `/` at every line break -- ` ( / ) `? Or is there a simpler solution? — ap21, Jan 04 '17 at 00:54
@ap21 the simpler solution is wrapping the whole expression in parentheses, as noted in my answer. — innisfree, Jan 04 '17 at 00:58

Importing Mathematica expression to Python correctly

1 Answers1