Hi All,
I was reading sympy crypto library where I am unable to understand
something in 'check_and_join' function.
def check_and_join(phrase, symbols=None, filter=None):
"""
Joins characters of `phrase` and if ``symbols`` is given, raises
an error if any character in ``phrase`` is not in ``symbols``.
Parameters
==========
phrase: string or list of strings to be returned as a string
symbols: iterable of characters allowed in ``phrase``;
if ``symbols`` is None, no checking is performed
Examples
========
>>> from sympy.crypto.crypto import check_and_join
>>> check_and_join('a phrase')
'a phrase'
>>> check_and_join('a phrase'.upper().split())
'APHRASE'
>>> check_and_join('a phrase!'.upper().split(), 'ARE', filter=True)
'ARAE'
>>> check_and_join('a phrase!'.upper().split(), 'ARE')
Traceback (most recent call last):
...
ValueError: characters in phrase but not symbols: "!HPS"
"""
*rv = ''.join(''.join(phrase))*
if symbols is not None:
symbols = check_and_join(symbols)
missing = ''.join(list(sorted(set(rv) - set(symbols))))
if missing:
if not filter:
raise ValueError(
'characters in phrase but not symbols: "%s"' % missing)
rv = translate(rv, None, missing)
return rv
>
This maybe very silly but use of join function twice is not clear to me.
Please if anyone could help. :)
Thanks in advance.
Aditya
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