in cassette/cassette_library.py [0:0]
def __getitem__(self, cassette_name):
"""Return the request from the loaded dictionary data."""
req = self.data.get(cassette_name, None)
if not req:
raise KeyError("Cassette '{c}' does not exist in \
library.".format(c=cassette_name))
req.rewind()
return req