send an in-memory chart object to Excel file

Question

Sorry, I’m a newbie so please be gentle. Is there a way to send an in-memory file (generated using Matplotlib) to an Excel file? I’m trying to do this using openpyxl but no luck. Any suggestions? Thanks!

I hacked on the following code to produce in-memory chart object:

import io
from PIL import Image
import matplotlib.pyplot as plt
plt.figure()
plt.plot([1, 2])
plt.title("test")
buf = io.BytesIO()
plt.savefig(buf, format='png')
buf.seek(0)
im = Image.open(buf)

wb = openpyxl.load_workbook('input.xlsx')
ws = wb.active


ws.add_image(im, 'A1')
wb.save('output.xlsx')

Unfortunately, this produced the following error message:
UnboundLocalError: local variable ‘rel’ referenced before assignment

Any suggestions would be greatly appreciated. Thanks!

Note: the following works but is inefficient.

wb = openpyxl.load_workbook('input.xlsx')
ws = wb.active
img = openpyxl.drawing.image.Image('my_chart.png')
ws.add_image(img, 'A1')
wb.save('output.xlsx')

Asked By: C.Hill

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Source

Answer 1

The problem is that the image handling code currently requires file paths. You can see where this is required if you look at the full traceback provided.

It’s actually no less efficient to use temporary files for the images instead of in-memory images so I’d advise doing this anyway.

Answered By: Charlie Clark

Answer 2

At least since v2.6.2 of openpyxl it is totally possible to insert in-memory images without requiring temporary file saving to fool the handling code. The problem was that add_image() needs the right Image object.
Here is the working code sample:

import io
#from PIL import Image
import matplotlib.pyplot as plt
from openpyxl.drawing.image import Image
plt.figure()
plt.plot([1, 2])
plt.title("test")
buf = io.BytesIO()
plt.savefig(buf, format='png')
buf.seek(0)
#im = Image.open(buf)
im = Image(buf)
im.anchor = 'A1'
wb = openpyxl.load_workbook('input.xlsx')
ws = wb.active
ws.add_image(im)
wb.save('output.xlsx')

Answered By: MacPara

Answer 3

Use io.ByteIO and penpyxl.drawing.image.Image to write picture data into an excel without any temporary disk storage.

import io
import openpyxl

book = openpyxl.Workbook()
sheet = book.active

# do something here

image     = io.BytesIO(your_picture_data)
image_xls = openpyxl.drawing.image.Image(image)
sheet.add_image(image_xls, 'A1')

# do something here

Answered By: wbwb

send an in-memory chart object to Excel file

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