From: Samu Mielonen [mailto:ex@uiah.fi] Sent: 25. oktober 1999 11:59 To: Alexander Staubo Cc: Zope Mailing List Subject: RE: Q: How to check if Image exists (inside REQUEST object)?

My question:

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You wouldn't know how to test if a REQUEST.image1 exists or not before actually using manage_addImage or manage_upload on that image?

Alexander Staubo [mailto:alex@mop.no] :

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Test on the content type of the file object, or check whether the file object's file attribute contains a non-zero file (eg., call seek(0, 2) and then check if tell() returns > 0).

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The following code illustrates the latter:

<dtml-if "REQUEST.has_key('MyFile')"> <dtml-if "(MyFile.file.seek(0, 2) or MyFile.file.tell()) > 0"> <!-- file is valid --> </dtml-if> </dtml-if>

Excellent! Thanks! It works. I don't yet understand how, but it works.

When ZPublisher receives an HTTP request, it builds the REQUEST variable from the request header. In the case of POSTs, in addition the header the request also contains a body. When using the multipart/form-data encoding type, this body follows a standard MIME format, wherein each piece of named data is bundled in a "multipart" attachment. Uploaded "files" have a content type, file name and binary contents, usually base64-encoded. For each such attachment, ZPublisher creates a FileObject instance (see lib/Python/ZPublisher/HTTPRequest.py). This FileObject has a filename attribute, a headers dictionary attribute, and a file attribute. The file attribute behaves like a standard Python file, and contains methods such as tell(), seek(), read() and so forth. Given such a variable MyFile, the Python expression (MyFile.file.seek(0, 2) or MyFile.file.tell()) > 0 will yield the value 1 if tell() returns > 0. The seek() doesn't return anything, so it will evaluate to None. This is handy shortcut in the Python language to make verbose tests more compact. It does not enhance readability, but reduces typing and in the context of Zope, faster than doing each operation separately. Anyway, a simpler test is checking the file name. Just testing whether the filename attribute is empty should do it. [snip]

Thanks again, Samu Mielonen

-- Alexander Staubo http://www.mop.no/~alex/ The difference between theory and practice is that, in theory, there is no difference between theory and practice.