# Calling sympy.stats.sample from SymPy.jl

**URL:** <https://discourse.julialang.org/t/calling-sympy-stats-sample-from-sympy-jl/53092>\
**Category:** General Usage\
**Tags:** pycall\
**Created:** [January 9, 2021, 6:14pm UTC](https://discourse.julialang.org/t/calling-sympy-stats-sample-from-sympy-jl/53092 "2021-01-09T18:14:29Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Brian\_Toomey](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/brian_toomey/32/20879_2.png) [@Brian\_Toomey](https://discourse.julialang.org/u/Brian_Toomey)\
**Post date:** [January 9, 2021, 6:14pm UTC](https://discourse.julialang.org/t/calling-sympy-stats-sample-from-sympy-jl/53092/1 "2021-01-09T18:14:29Z")

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Hi Julia discourse – this forum (and Julia) seems so great I thought I would stop lurking.

I’ve been looking at how to interact with sympy.stats using SymPy.jl. The author of the package was kind enough to give some initial tips.  
[here](https://github.com/jverzani/SymPy.jl/issues/5).

This works great with the exception of the `sample` function which returns the below. I’m not groking this error – how would I sample from this random variable?

```julia
using SymPy, PyCall;
SymPy.PyCall.pyimport_conda("sympy.stats", "sympy")
@vars Z

Z = sympy.stats.Normal("Z", 0, 2)
sympy.stats.E(Z) # returns 0

sympy.stats.sample(Z) # returns the below

/Users/toomey8/.julia/conda/3/lib/python3.8/site-packages/sympy/stats/rv.py:1104: UserWarning:
The return type of sample has been changed to return an iterator
object since version 1.7. For more information see
https://github.com/sympy/sympy/issues/19061
  warnings.warn(filldedent(message))
PyObject <generator object sample_iter.<locals>.return_generator_finite at 0x7fb8b1380f20>

```

How would I get it to return a sample from the random variable?

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<div class="post-metadata">

**Author:** ![stillyslalom](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stillyslalom/32/45687_2.png) [@stillyslalom](https://discourse.julialang.org/u/stillyslalom)\
**Post date:** [January 9, 2021, 11:38pm UTC](https://discourse.julialang.org/t/calling-sympy-stats-sample-from-sympy-jl/53092/2 "2021-01-09T23:38:56Z")

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> [@Brian\_Toomey](#):
>
> `sympy.stats.sample(Z) # returns the below`

Looking at the [linked PR](https://github.com/sympy/sympy/pull/19342#issuecomment-629927422), it appears you need to treat the object as an iterator:

```julia
julia> py"next"(sympy.stats.sample(Z))
-1.7527355361953159

julia> py"next"(sympy.stats.sample(Z, size=3))
3-element Vector{Float64}:
 -1.0020213130043105
  1.1586894921503135
  0.3896799828295135

```

Of course, if all you need to do is sample from a normal distribution, you can use Distributions.jl (which should be much faster than calling Python) or Julia’s builtin `randn`:

```julia
julia> using Distributions, BenchmarkTools

julia> @btime py"next"(sympy.stats.sample($Z))
  442.900 μs (15 allocations: 624 bytes)
-0.427252225353338

julia> Zⱼ = Normal(0, 2.0)
Normal{Float64}(μ=0.0, σ=2.0)

julia> @btime rand($Zⱼ)
  8.400 ns (0 allocations: 0 bytes)
0.6076344626588824

julia> @btime 2randn()
  7.900 ns (0 allocations: 0 bytes)
1.4214944284831204

```

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<div class="post-metadata">

**Author:** ![Brian\_Toomey](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/brian_toomey/32/20879_2.png) [@Brian\_Toomey](https://discourse.julialang.org/u/Brian_Toomey)\
**Post date:** [January 11, 2021, 2:23pm UTC](https://discourse.julialang.org/t/calling-sympy-stats-sample-from-sympy-jl/53092/3 "2021-01-11T14:23:13Z")

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Thank you. This is absolutely perfect. Good to know about doing something similar with the Distributions package too. Appreciated on all counts!

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<div class="post-metadata">

**Author:** ![j\_verzani](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/j_verzani/32/8551_2.png) [@j\_verzani](https://discourse.julialang.org/u/j_verzani)\
**Post date:** [January 11, 2021, 4:01pm UTC](https://discourse.julialang.org/t/calling-sympy-stats-sample-from-sympy-jl/53092/4 "2021-01-11T16:01:11Z")

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Thanks for pointing this out. A few things for future readers:

- I was also getting a message about failing to import`scipy`, so added `scipy`: `SymPy.PyCall.pyimport_conda("scipy", "scipy")`. (Not sure this was needed)
- In place of `py"next"(...)` you can call `collect` on the iterator, as in: `collect(sympy.stats.sample(Z, numsamples=3))`. (This is used elsewhere with python sets, so hopefully is more idiomatic).