45 行 Python 代码写一个语言检测器

class NGram(object):
def __init__(self, text, n=3):
self.length = None
self.n = n
self.table = {}
self.parse_text(text)
self.calculate_length()

def parse_text(self, text):
chars = ' ' * self.n # initial sequence of spaces with length n

for letter in (" ".join(text.split()) + " "):
chars = chars[1:] + letter # append letter to sequence of length n
self.table[chars] = self.table.get(chars, 0) + 1 # increment count

def calculate_length(self):
""" Treat the N-Gram table as a vector and return its scalar magnitude
to be used for performing a vector-based search.
"""
self.length = sum([x * x for x in self.table.values()]) ** 0.5
return self.length

def __sub__(self, other):
""" Find the difference between two NGram objects by finding the cosine
of the angle between the two vector representations of the table of
N-Grams. Return a float value between 0 and 1 where 0 indicates that
the two NGrams are exactly the same.
"""
if not isinstance(other, NGram):
raise TypeError("Can't compare NGram with non-NGram object.")

if self.n != other.n:
raise TypeError("Can't compare NGram objects of different size.")

total = 0
for k in self.table:
total += self.table[k] * other.table.get(k, 0)

return 1.0 - (float(total) )/ (float(self.length) * float(other.length))

def find_match(self, languages):
""" Out of a list of NGrams that represent individual languages, return
the best match.
"""
return min(languages, lambda n: self - n)


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