I have been working through Hilpisch's "Python for Finance" and haven't had much trouble until I got to the chapter on writing to Excel. I am running Python 3.5 and using the OpenPyxl module

```
import openpyxl as oxl
import numpy as np 
wb = oxl.Workbook()
ws = wb.create_sheet(index = 0, title = 'oxl_sheet')
data = np.arange(1, 65).reshape((8, 8))
for c in range(1, data.shape[0]):
    for r in range(1, data.shape[1]):
        ws.cell(row=r, column=c, value=data[c, r])

```

This returns: `ValueError: Cannot convert 10 to Excel`

Is it an issue with using numpy? For example, the following code returns a similar error.

```
ws.cell(row=1, column=1, value=data[0,0])

```

But replacing `data[0, 0]` with an integer or float raises no problem.

Seems like there should be an easy fix to this.