Implementation method of detecting rare words in Python

Solution ideas

The first thing that comes to mind is to use python’s regular expressions to match illegal characters and then find illegal records. However, ideals are always full, but reality is cruel. During the implementation process, I discovered that I lacked knowledge about character encoding and Python's internal string representation. During this period, I went through a lot of pitfalls, and although there were still some ambiguities in the end, I finally had an overall clear understanding. Record your experience here to avoid falling in the same place in the future.

The following test environment is the python 2.7.8 environment that comes with ArcGIS 10.3. There is no guarantee that other python environments will also be suitable.

python regular expression

The regular function in python is provided by the built-in re function library, which mainly uses 3 functions. re.compile() Provides reusable regular expressions, match() and search() functions return matching results. The difference between the two is: match() starts matching from the specified position, search() will search backward from the specified position until a matching string is found. For example, in the code below, match_result starts matching from the first character f, and returns a null value if the match fails; search_result searches backward from f until it finds the first matching character a, and then uses the group() function The output matching result is the character a.

import re

pattern = re.compile('[abc]')
match_result = pattern.match('fabc')
if match_result:
 print match_result.group()

search_result = pattern.search('fabc')
if search_result:
 print search_result.group()

pattern = re.compile(r'[~!@#$%^&* ]')

pattern = re.compile(r'[~!@#$%^&* ]|[^\xA1-\xF7][^\xA1-\xFE]')

import re

def is_rare_name(string):
 pattern = re.compile(u"[~!@#$%^&* ]")
 match = pattern.search(string)
 if match:
 return True

 try:
    string.encode("gb2312")
  except UnicodeEncodeError:
   return True

  return False