Fabrice Schlegel - 5 months ago 22

Python Question

I would like to iterate through a series of numpy arrays whose variable names look like

`numpy_array_001, numpy_array_002, ... numpy_array_N`

To add them up, I'm looking for something like:

`sum += "numpy_array_"+str(number)`

The issue with the above is that

`"num_pyarray_"+str(number)`

How can I rewrite this last line to add the arrays together?

The expected outcome is

`sum = numpy_array_001 + numpy_array_002+ ... + numpy_array_N`

for any N

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Answer Source

I'm sorry, I think you'll have to use the `eval`

function for this.

Here's a simple example in which I have three variables (`x1`

, `x2`

, `x3`

) and I add them up:

```
x1 = 1
x2 = 2
x3 = 3
# Make an string containing the expression to evaluate
expr=''
for i in range(3):
expr = expr + 'x' + str(i+1) + ' + '
expr = expr[0:-3] # remove the last ' + '
# Show the expression, and evaluate it
print(expr)
eval(expr)
```

You can adapt this to do `sum +=`

instead. So something like:

```
for i in range(N):
eval('sum += numpy_array_' + '{:03}'.format(i+1)')
```

But really, if you have any control over this, you should design your program such that it *doesn't* store a bunch of arrays in separate variables like that. That's just making life difficult for yourself.

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