handling compression: filename vs magic numbers
biopython/biopython#1686 is discussing reading in compressed files. pandas handles this pretty nicely (never run into issues myself), but it looks like the code infers the compression from the file extension. 

https://github.com/pandas-dev/pandas/blob/v0.23.1/pandas/io/common.py#L238

Why do this over sniffing for the magic number and inferring from there? If there was discussion about this in the past, could you point me to the relevant issue/email (I tried searching the issue tracker without luck)?