# How to Call Python From Mathematica, Including NumPy

### A tutorial on how to use two popular and powerful languages for data manipulation and data science together.

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Join For FreeThe Mathematica function `ExternalEvalute`

lets you call Python from Mathematica. However, there are a few wrinkles.

I first pasted in an example from the Mathematica documentation and it failed.

```
ExternalEvaluate[
"Python",
{"def f(x): return x**2", "f(3)"}
]
```

It turns out you (may) have to tell Mathematica where to find Python. I ran the following, tried again, and the example worked.

```
RegisterExternalEvaluator[
"Python",
"C:\\bin\\Anaconda3\\python.EXE"
]
```

You can also run Python with NumPy loaded using

` ExternalEvaluate["Python-NumPy", ... ]`

except that didn't work the first time either. You have to register a `Python-NumPy`

evaluator separately. So I ran

```
RegisterExternalEvaluator[
"Python-NumPy",
"C:\\bin\\Anaconda3\\python.EXE"
]
```

and then tried again calling Python code using NumPy. But then there's the question of how it imports NumPy. Does it simply run `import numpy`

, or maybe `from numpy import *`

, or maybe `import numpy as np`

? It turns out the first possibility is what happens. So to print `pi`

from NumPy, your code string needs to be `numpy.pi`

.

You don't need to use `Python-NumPy`

if you just do your own importing. For example, this code returns π².

```
ExternalEvaluate[
"Python",
"import numpy; x = numpy.pi; x**2"
]
```

And you can import any library you'd like, not just NumPy.

```
ExternalEvaluate[
"Python",
"from sympy import isprime; isprime(7)"
]
```

Everything above applies to Mathematica 11.3 and Mathematica 12.

Published at DZone with permission of John Cook, DZone MVB. See the original article here.

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