1. ravel and flatten

The difference is that flatten always returns a copy and ravel returns a view of the original array whenever possible. This isn’t visible in the printed output, but if you modify the array returned by ravel, it may modify the entries in the original array. If you modify the entries in an array returned from flatten this will never happen. ravel will often be faster since no memory is copied, but you have to be more careful about modifying the array it returns.

2. reshape and resize

The resize method works just like the reshape method, but modifies the
array it operates on

3. Dates

3.1 converters

converters : dict, optional
A dictionary mapping column number to a function that will convert
that column to a float. E.g., if column 0 is a date string:
converters = {0: datestr2num}. Converters can also be used to
provide a default value for missing data (but see also genfromtxt):
converters = {3: lambda s: float(s.strip() or 0)}. Default: None.

3.2 binary to str

ValueError: could not convert string to float: b’28-01-2011’

TypeError: strptime() argument 1 must be str, not bytes