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In http.client.HTTPConnection's send(data) method if data has attribute read after is handled correctly as file-like object and sent out successfully the code continues to what should be an else branch (~line 858) and tries to send out again the data. This is harmless in most situations but only by chance and also run's unnecessary code.
I propose either to use an else branch for the code after line 858 or simply instead break return at line 853.
Cheers,
Sanyi

Renamed the report since it's unsafe for sure.
This problem was previously called: Avoid unnecessary and possibly unsafe code from http.client.HTTPConnection.send. 
Imagine that the data parameter from HTTPConnection it's a file like object but it's not iterable, maybe some custom data wrapper.
the if hasattr(data, "read"): True branch will correctly send out the response then unnecessary continue to:
try:
 self.sock.sendall(data)
 except TypeError:
 if isinstance(data, collections.Iterable):
 for d in data:
 self.sock.sendall(d)
 else:
 raise TypeError("data should be a bytes-like object "
 "or an iterable, got %r" % type(data))
and crash!

Seems this bug was fixed in issue16658.