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numpy.core.defchararray.chararray.isalnum
method
chararray.isalnum()[source]- 
    
Returns true for each element if all characters in the string are alphanumeric and there is at least one character, false otherwise.
See also
char.isalnum 
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 https://docs.scipy.org/doc/numpy-1.16.1/reference/generated/numpy.core.defchararray.chararray.isalnum.html