The International Statistical Classification of Diseases and Related Health Problems¹ (ICD) is a list of the World Health Organization² (WHO) containing more than 10.000 diseases and maladies that patients might present. In addition to a description, each disease or malady is also given a unique ICD-code that the medical community uses for record-keeping. For example, a patient admitted to the hospital with whooping cough would be logged in the database with ICD-code A37.

Some of the stranger complaints that can be found on the list:

However, without any doubt our favorite so far is "Burn due to water-skis on fire" (V91.07). It's a dangerous world. Be safe out there.

Assignment

The Hippocrates code is a cryptographic technique that makes use of ICD-codes. A message is encrypted by replacing each character with a Hippocrates-code of the form

<ICD-code>.$$n$$    ($$n \in \mathbb{N}$$)

The Hippocrates-code is chosen so that the $$n$$-th position in the description of the ICD-code is occupied by the encoded character. The positions of the characters are numbered from zero. The Hippocrates-codes are separated by a single space in the ciphertext. This way, the message

Eat wise, drop a size

is encrypted as

A75.0.0 K50.119.59 T43.2.75 V14.1.21 V42.1.54 E10.32.53 T21.70.5 T21.06.12 S59.239.62 M85.812.56 M85.812.34 Q95.3.27 V64.0.22 T37.3.61 S00.261.34 T49.4X6.76 F44.6.32 A02.24.23 V59.9.62 J10.89.41 O91.1.13

We see, for example, that the first letter (position 0) in the description of ICD-code A75.0 (Epidemic louse-borne typhus fever due to Rickettsia prowazekii) is occupied by the uppercase letter E and that a lowercase letter a occurs at position 59 in the description of ICD-code K50.119 (Crohn's disease of large intestine with unspecified complications). When encoding, uppercase and lowercase letters are considered different characters, and the spaces and punctuation marks are also replaced by a corresponding Hippocrates-code.

However, the encoding is not unique because the same character may occur at multiple positions and in multiple descriptions. As such, the same sentence may also be encoded as

W92.XXXD.0 I97.611.84 I97.611.38 S59.099.31 M90.832.38 V42.1.93 M61.25.29 I67.83.43 T37.92.67 W93.38 O22.23 V59.9.48 F04.23 C34.2.13 F44.6.43 A00.0.28 M85.812.5 A02.24.23 Z96.621.21 J10.89.41 N07.9.31

Your task is to define a class Hippocrates that can be used to encode and decode messages using to the Hippocrates code. When creating objects of the class Hippocrates, the location (str) of a text file must be passed. Each line of the text file contains an ICD-code and the corresponding description, separated by a single space. These are the ICD-codes that are used for encoding and decoding. An ICD-code never contains spaces (dots are allowed). Make sure the class Hippocrates supports at least the following methods:

• A method description that takes an ICD-code (str). The method must return the description (str) that corresponds to the given ICD-code. If the given ICD-code does not occur in the text file that was passed when creating the object, a ValueError must be raised with the message invalid ICD-code.

• A method character that takes a Hippocrates-code (str). The method must return the character (str) that is replaced by the given Hippocrates-code in the cryptographic technique. If the ICD-code in the given Hippocrates-code does not occur in the text file that was passed when creating the object or if the corresponding description does not contain an $$n$$-the character, a ValueError must be raised with the message invalid Hippocrates-code.

• A method codes that takes a character (str). The method must return a set (set) containing all Hippocrates-codes (str) by which the given character might be replaced in the cryptographic technique. Make sure an empty set is returned in case no Hippocrates-code can replace the given character.

• A method encode that takes a plaintext (str). The method must return a ciphertext (str) for the given plaintext, where encoding is based on the Hippocrates code. Each character of the plaintext must be replaced by randomly choosing among all possible Hippocrates-codes that encode the character. If the given plaintext contains characters that cannot be encoded by a Hippocrates-code, a ValueError must be raised with the message invalid plaintext.

• A method decode that takes a ciphertext (str), where encoding is based on the Hippocrates code. The method must return the corresponding plaintext (str). In case the argument is no valid ciphertext for the Hippocrates code, a ValueError must be raised with the message invalid ciphertext.

Example

In the following interactive session we assume the text file ICD.txt³ to be located in the current directory.

>>> codec = Hippocrates('ICD.txt4')
>>> codec.description('A00')
'Cholera'
>>> codec.description('A00.0')
'Cholera due to Vibrio cholerae 01, biovar cholerae'
>>> codec.description('A00.2')
Traceback (most recent call last):
ValueError: invalid ICD-code
>>> codec.character('A00.0')
'C'
>>> codec.character('A00.2')
'o'
>>> codec.character('A00.0.33')
','
>>> codec.character('A00.2.33')
Traceback (most recent call last):
ValueError: invalid Hippocrates-code
>>> codec.codes('V')
{'O22.0', 'A00.1.15', 'I83.218.0', 'A00.0.15'}
>>> codec.codes('v')
{'I67.83.12', 'V59.9.50', 'V64.0.76', 'H59.121.12', 'M50.022.3', 'S44.8X9.19', 'T37.92.46', 'S44.8X9.51', 'V42.1.68', 'S66.911.68', 'T37.3.16', 'T37.1X.16', 'V04.92.67', 'M67.971.28', 'B08.04.4', 'Q95.3.53', 'V49.60.69', 'V64.0.3', 'T43.2.16', 'V64.0.26', 'E10.32.49', 'B57.30.40', 'A00.0.38', 'V64.0.13', 'I89.9.10', 'I83.218.9', 'V04.92.54', 'F44.6.3', 'I89.9.35', 'W24.0.23', 'M67.232.4', 'B57.30.43', 'S90.464.16', 'N13.9', 'V52.1.88', 'S14.9.25', 'V52.1.30', 'S78.922.54', 'V92.16.45', 'V14.1.51', 'S00.261.16', 'B57.30.28', 'V59.9.13', 'W93.19', 'W92.XXXD.19', 'V64.0.63', 'M50.022.34', 'J10.89.44', 'A00.1.38', 'A75.0.30', 'V14.1.64', 'T37.1X5.2'}
>>> codec.codes('.')
{'Z68.35.29', 'Z68.35.24', 'Z68.42.29', 'Z68.36.29', 'Z68.42.24', 'Z68.36.24', 'Z68.43.27'}
>>> codec.codes('xxx')
set()
>>> codec.codes('!')
set()
>>> codec.encode('Eat wise, drop a size')
'A75.0.0 K50.119.59 T43.2.75 V14.1.21 V42.1.54 E10.32.53 T21.70.5 T21.06.12 S59.239.62 M85.812.56 M85.812.34 Q95.3.27 V64.0.22 T37.3.61 S00.261.34 T49.4X6.76 F44.6.32 A02.24.23 V59.9.62 J10.89.41 O91.1.13'
>>> codec.encode('Eat wise, drop a size')
'W92.XXXD.0 I97.611.84 I97.611.38 S59.099.31 M90.832.38 V42.1.93 M61.25.29 I67.83.43 T37.92.67 W93.38 O22.23 V59.9.48 F04.23 C34.2.13 F44.6.43 A00.0.28 M85.812.5 A02.24.23 Z96.621.21 J10.89.41 N07.9.31'
>>> codec.encode('Eat wise, drop a size!')
Traceback (most recent call last):
ValueError: invalid plaintext
>>> codec.decode('A75.0.0 K50.119.59 T43.2.75 V14.1.21 V42.1.54 E10.32.53 T21.70.5 T21.06.12 S59.239.62 M85.812.56 M85.812.34 Q95.3.27 V64.0.22 T37.3.61 S00.261.34 T49.4X6.76 F44.6.32 A02.24.23 V59.9.62 J10.89.41 O91.1.13')
'Eat wise, drop a size'
>>> codec.decode('W92.XXXD.0 I97.611.84 I97.611.38 S59.099.31 M90.832.38 V42.1.93 M61.25.29 I67.83.43 T37.92.67 W93.38 O22.23 V59.9.48 F04.23 C34.2.13 F44.6.43 A00.0.28 M85.812.5 A02.24.23 Z96.621.21 J10.89.41 N07.9.31')
'Eat wise, drop a size'
>>> codec.decode('X6.6.6 Q99.9.9 Z12.34')
Traceback (most recent call last):
ValueError: invalid ciphertext