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I have a problem how to get values from pytables. Values are bit based, but stored as integer number.

One column in my table is Int32Column() with name 'Value'. In this column I will store integer values where every bit has different meaning. So, if I want information for some bit, I will take value from table and make some bit manipulation actions. I don't know how to make query for getting specified values from table.

For example, I want to know all values in Value column where is first bit == 1 and third bit ==1.

How to make that query? I'm trying with mask:

[ x['Value'] for x in table.where('((Value & mask) == mask)')]

but, I'm getting exception:

NotImplementedError: unsupported operand types for \*and\*: int, int

Processing query must be very fast because large number of rows in future. One restriction is that values must be as int values in table, because I'm getting values from server in int format. I hope that someone has better solution.

Wilduck
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Nikola Stevanovic
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1 Answers1

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For future reference.

I had a similar problem and solved it in the following way. As the usual bitwise operators(<<, >>) are not available and the meaning of the &, | operators is logical, instead of bitwise, one has to improvise.

To check if a value VAL has the n-th bit set or not, we can shift the interesting bit to the 0th position, which denotes the parity of the number (2**0). The parity can be checked using the modulus operator. So, one can do something like to check whether, for example, bit 25 is set and 16 is unset.

table.where("((VAL/(2**25))%2==1) & ((VAL/(2**16))%2==0)")

Not elegant, but working for now.

Joosep Pata
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