@Tom-TBT I tried to reproduce the issue using the following example code:

from omero.gateway import BlitzGateway

with BlitzGateway(
        host='localhost', username=<username>, passwd=<password>) as conn:
    conn.connect()
    conn.SERVICE_OPTS['omero.group']='-1'

    i=conn.getObject('Image',185001)
    print(i.getPixelSizeX())
    print(i.getPixelSizeX(units="MICROMETER"))

All OMERO.py versions between 5.13.0 and 5.19.5 produced the following output:

0.5933762649494021
0.5933762649494021 MICROMETER

Older versions failed to connect due to SSL issues.

Matching your code history review, it looks like this has been the behavior of the API for the last decade. Do you have more specifics on which version of OMERO.py would have been returning the Length object by default? Or is the issue not about the getPixelSize API but rather the image_to_html?

Hi @sbesson, thank you for the thorough testing.

It seems to me that something changed about image.getPixelSizeX() (and Y and Z)

I was wrong, nothing changed then. As you say it's just about image_to_html

I checked in the history of commit in the PR and the last commit introduced the error, that was not shown in the screenshots above.
The commit b0a7fad replaced
{image.getPixelSizeX(units=True).getUnit()}
with
UnitX = image.getPixelSizeX().getUnit()

thus getting a float instead of the expected omero.model.LengthI.

Adding back units=True gave me the expected output:

@jo-mueller could you add that to your current fixing PR?
I can open another PR myself, sorry. This is different enough from that PR
#429

def image_to_html(image):
    import base64

    try:
        pixsizeX = '{:.3f}'.format(image.getPixelSizeX())
        pixsizeY = '{:.3f}'.format(image.getPixelSizeY())
        pixsizeZ = '{:.3f}'.format(image.getPixelSizeZ())
        UnitX = image.getPixelSizeX(units=True).getUnit()
        UnitY = image.getPixelSizeY(units=True).getUnit()
        UnitZ = image.getPixelSizeZ(units=True).getUnit()
    except:
        pixsizeX, pixsizeY, pixsizeZ = 'na', 'na', 'na'
        UnitX, UnitY, UnitZ = 'na', 'na', 'na'