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Counting weekdays between dates

Need a method to accurately count the number of weekdays between two days? [The key here is "accurately", it is a bit harder than it seems at first]. In Python there are several ways to do this, but most involve some iteration or list comprehension. In my opinion, if you have to do that, you are probably violating the Python idiom of "use the batteries".

If a record exists

A common action when synchronizing data between some source and a database is to check if such-and-such record already exists and needs to be updated or if a new record needs to be created. The SQLAlchemy's one() method [of the query object] provides an easy way to check to see if such-and-such record exists; but it doesn't return either an ORM object or None - if no record is found it raises an exception. This is surprising at first as x=do;if-not-x is possibly the most common of all Python constructs.

A JSONDateTime TypeDecorator

JSON doesn't provide a date or date-time construct; therefore every application is burdened with implementing a solution of it's own for receiving date-time information over the wire. On common issue receiving JSON and serializing that data into some type of database - but the database knows the value is a date-time and you want to be able to perform date-time like operations on the value (locally).

Discovering DLL Version With pefile

A Microsoft KB article claimed that if a specific DLL was at least a certain version that a bug reported by one of my users would be resolved. But the user was using their computer and I dislike interrupting people's work (I know how annoying it is when someone interrupts me). No problem; I can just grab the named DLL off their machine over the network and copy it to my home directory. But I'm not running Windows and all file tells me is that the DLL is a 32-bit PE file.

Printing Via LPR

If you have a Python app, or almost any kind of app, the accepted manner for printing is to use some kind of subprocess to invoke some command-line utility to submit the print job. Of course this requires that the underlying subsystems are aware of printers [and thus run a printer subsystem]. It also assumes the name of the command-line utility, the permissions are adequate to execute it, and all manner of other things. To put it simply: this is terrible! Why does my web server, workflow server, etc... need to run a print service?

SQLAlchemy & Upcoming Birthdays

OpenGroupware Coils uses SQLAlchemy as it's ORM. One of the desired features was a Logic command that efficiently returns contacts with upcoming birthdays. In raw SQL this query would be very simple to write - but how to do it in SQLAlchemy? The answer: sql.expression.extract which will create an expression column equivalent to EXTRACT. With EXTRACT it is possible to compare to the year-of-day represented by a date. The Python code looks like:

XSLT Transform to TXT, with LXML

Maybe this should be obvious, but it wasn't to me. I've got an XML document and an XSLT stylesheet. But that stylesheet just produces text, not XML; it is essentially a template for an e-mail. So I was extending OIE's transformAction for performing XSLT transforms that produce other than XML... but the documentation is a bit thin and every example is XML results. The trick is pretty simple, just

unicode(result)

and make sure [of course] that you have

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