Reading a real tag - possible issue?

[sdmolt]

Couldn't find anything on this one - When reading a REAL tag, I get a number back that is slightly off - for example:

1. real_tag in PLC = -0.1, pycomm3 reads: Tag(tag='real_tag' value=-0.10000000149011612, type='REAL', error=None)
2. real_tag in PLC = -0.01, pycomm3 reads: Tag(tag='real_tag', value=0.009999999776482582, type='REAL', error=None)

I also noticed the responses in the docs (basic read/write examples), your response for the real was Tag(tag='REAL1', value=100.0009994506836, type='REAL', error=None) - was that the actual value in the processor?

[ottowayi]

Yeah that is because of how floating points are represented in binary. Here is a doc that explains more about how Python handles floats. The plc is doing some rounding to show you the closest approximate value and python does the same when you type .1 or 1/10. But, since I'm using the struct module to unpack the floating point value from bytes, I don't think it will do the rounding for the string representation. One thing I could do is change the repr for the Tag objects to round to a certain number of decimal places, but then it would be to a fixed number of decimals for every object.

[sdmolt]

I think the way it is now is probably good rather than defining a decimal count. I can do the rounding outside of pycomm3. Thanks for the fast response!