Read Azure Storage blob into matplotlib

Question

I'm working with matplotlib.pyplot and Azure Storage blobs (azure.storage.blob) in a Azure Functions environment (should not access the file system).

My goal is to get a blob:

service = blob.BlobServiceClient(account_url="https://mysa.blob.core.windows.net", credential=SA_PRIMARY_KEY)
blob_client = service.get_blob_client(container="mycontainer", blob="myimg.JPG")
blob_data = blob_client.download_blob()

And open it with pyplot using imread like:

img = plt.imread(blob_data_to_read_opened_stream, format="JPG")

So I think I'm missing a piece. After obtaining the blob_data object it's needed to copy it's content into a stream passing it to pyplot

with open("./BlockDestination.jpg", "wb") as blob_stream:
    blob_data = blob.download_blob()
    blob_data.readinto(blob_stream)
    img = plt.imread(blob_stream, format="JPG")

This would fail cause imread needs a

file-like object opened in read-binary mode

How can I achieve my goal without opening two different streams?

Answer 1

You can generate a SAS token and use it to read images from your storage account directly instead of download images and read them. It will ease the server pressure and only one read stream here. Just try the code below:

from azure.storage.blob import ResourceTypes, AccountSasPermissions, generate_account_sas,BlobServiceClient
from datetime import datetime, timedelta
import matplotlib.pyplot as plt
import matplotlib.patches as patches
import matplotlib.cbook as cbook

connStr = '<storage account connection string>'
containerName ='<container name>'
blobName = "<image name>"

blob_service_client = BlobServiceClient.from_connection_string(connStr)

sas_token = generate_account_sas(
    blob_service_client.account_name,
    account_key=blob_service_client.credential.account_key,
    resource_types=ResourceTypes(object=True),
    permission=AccountSasPermissions(read=True),
    expiry=datetime.utcnow() + timedelta(hours=1)
)

destImageUrl = blob_service_client.primary_endpoint + containerName + "/" + blobName + "?" + sas_token

image  = plt.imread(destImageUrl , format="JPG")

fig, ax = plt.subplots()
im = ax.imshow(image)
patch = patches.Circle((260, 200), radius=200, transform=ax.transData)
im.set_clip_path(patch)

ax.axis('off')
plt.show()

My .jpg file content:

Result: