# How to call SymPy Python function linear\_eq\_to\_matrix
**URL:** https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960
**Category:** General Usage
**Tags:** pycall
**Created:** [July 19, 2017, 10:33pm UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960 "2017-07-19T22:33:42Z")
**Posts on this page:** 7
**Page:** 1
### Author:  [@jman87](https://discourse.julialang.org/u/jman87)
#### Post date: [July 19, 2017, 10:33pm UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/1 "2017-07-19T22:33:42Z")
I’m using SymPy in Julia to solve a system of equations and I would like to be able to call the SymPy function linear\_eq\_to\_matrix as documented on this page: [http://docs.sympy.org/latest/modules/solvers/solveset.html](http://docs.sympy.org/latest/modules/solvers/solveset.html)
I have a Python script containing the following code that uses the function:
```python
#!/usr/local/bin/python
from sympy import *
x, y, z = symbols('x y z')
eqns = [x + 2*y + 3*z - 1, 3*x + y + z + 6, 2*x + 4*y + 9*z - 2]
print("eqns = ", eqns)
A, b = linear_eq_to_matrix(eqns, [x, y, z])
print("A = ", A)
print("b = ", b)
```
When I run this, I get the expected output:
```python
eqns = [x + 2*y + 3*z - 1, 3*x + y + z + 6, 2*x + 4*y + 9*z - 2]
A = Matrix([[1, 2, 3], [3, 1, 1], [2, 4, 9]])
b = Matrix([[1], [-6], [2]])
```
Now, when I try to do the same thing in Julia, I have tried the following input file:
```julia
#!/usr/local/bin/julia
using SymPy
@vars x y z
eqns = ([x + 2*y + 3*z - 1, 3*x + y + z + 6, 2*x + 4*y + 9*z - 2])
println("eqns = ", eqns)
A, b = linear_eq_to_matrix(eqns, ([x, y, z]))
println("A = ", A)
println("b = ", b)
```
But this fails with the following output/error:
```julia
eqns = SymPy.Sym[x + 2*y + 3*z - 1, 3*x + y + z + 6, 2*x + 4*y + 9*z - 2]
ERROR: LoadError: UndefVarError: linear_eq_to_matrix not defined
Stacktrace:
[1] include_from_node1(::String) at ./loading.jl:569
[2] include(::String) at ./sysimg.jl:14
[3] process_options(::Base.JLOptions) at ./client.jl:305
[4] _start() at ./client.jl:371
while loading /...path_to_my_file.../juliaTest.jl, in expression starting on line 10
```
I have tried to figure out how to use PyCall or something similar to directly call this function but with no success. I have confirmed that I am calling/using the same versions of Python/SymPy in Julia so that’s not the issue. I have also confirmed that the SymPy function “solveset” which is documented on the link I provided above does work as expected in both Julia and Python, so it seems like Julia should be able to call “linear\_eq\_to\_matrix” somehow, even if it’s a bit clunky.
Can someone please show me how to do this? Thanks.
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [July 19, 2017, 11:20pm UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/2 "2017-07-19T23:20:50Z")
Apparently that function isn’t explicitly wrapped by SymPy, but you can call the Python function directly by:
```julia
A, b = SymPy.sympy["linear_eq_to_matrix"](eqns, x, y, z)
```
---
### Author:  [@jman87](https://discourse.julialang.org/u/jman87)
#### Post date: [July 19, 2017, 11:43pm UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/3 "2017-07-19T23:43:06Z")
I just noticed that using either [“linear\_eq\_to\_matrix”] or [:linear\_eq\_to\_matrix] will work.
Would it be possible for you to comment on why either syntax is acceptable? And help me know if there are certain times I would need to use one or the other?
If I need to start a new topic for this though that’s fine too.
Thanks so much for your help! 😃
---
### Author:  [@mohamed82008](https://discourse.julialang.org/u/mohamed82008)
#### Post date: [July 20, 2017, 2:52am UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/4 "2017-07-20T02:52:16Z")
I am pretty sure the difference is negligible. You can always use `@time` before the function to see which one takes slightly longer. And by negligible, I mean you should only worry about it if you use it in a humongous loop in which case you should be far more concerned with SymPy’s slowness, because it is written in Python, than with the difference between the 2 PyCall syntaxes.
---
### Author:  [@stevengj](https://discourse.julialang.org/u/stevengj)
#### Post date: [July 20, 2017, 3:17am UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/5 "2017-07-20T03:17:57Z")
> [@jman87](#):
>
> I just noticed that using either `["linear_eq_to_matrix"]` or `[:linear_eq_to_matrix]` will work. Would it be possible for you to comment on why either syntax is acceptable?
Either syntax works. As explained in the [PyCall README](https://github.com/JuliaPy/PyCall.jl#pyobject), doing `foo[:bar]` or `foo["bar"]` are both analogous to `foo.bar` in Python, but `foo[:bar]` will try to convert the result to a native Julia type if possible while `foo["bar"]` will always return a `PyObject`. Whenever I have something that I know returns a function/method object, which will get left as a `PyObject` anyway, I tend to use `foo["bar"]` to avoid the type-introspection step, but in most cases it won’t make a noticeable performance difference.
---
### Author:  [@jman87](https://discourse.julialang.org/u/jman87)
#### Post date: [July 20, 2017, 1:29pm UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/6 "2017-07-20T13:29:16Z")
Excellent. Thanks for the quick and very helpful feedback guys. Code on!
---
### Author:  [@j\_verzani](https://discourse.julialang.org/u/j_verzani)
#### Post date: [July 20, 2017, 3:51pm UTC](https://discourse.julialang.org/t/how-to-call-sympy-python-function-linear-eq-to-matrix/4960/7 "2017-07-20T15:51:55Z")
If speed isn’t an issue, I have a PR adding a `sympy_str` macro, so that you can call this as `sympy"linear_eq_to_matrix"(...)`. The advantage is this will check beyond the `sympy` module to try and resolve the call, which is needed for some calls.