仅当带空格，句点或什么都没有正则表达式时，才使用Python匹配字符串中的字母吗？

Question

I am trying to write this code for readability but the last 'for x in measurements' clearly doesn't work.

The following prints ' t' but I don't want it to match on ' test'
I do want it to match on ' t' of 'this is at' if it were a test case.

Possible without resorting to regex?

measurements = ['t', 'tsp', 'T', 'tbl', 'tbs', 'tbsp', 'c']
measurements = ([' ' + x + ' ' for x in measurements] + #space on either side
                [' ' + x + '.' for x in measurements] + #space in front, period in back
                [' ' + x + '' for x in measurements])   #space in front, nothing in back???

string_to_check = 'this is a test'

for measurement in measurements:
    if measurement in string_to_check:
        print(measurement)

Answer 1

Here you could use re.search

>>> measurements = ['t', 'tsp', 'T', 'tbl', 'tbs', 'tbsp', 'c']
>>> measurements = ([' ' + x + ' ' for x in measurements] + [' ' + x + '\.' for x in measurements] + [' ' + x + r'\b' for x in measurements])
>>> measurements
[' t ', ' tsp ', ' T ', ' tbl ', ' tbs ', ' tbsp ', ' c ', ' t\\.', ' tsp\\.', ' T\\.', ' tbl\\.', ' tbs\\.', ' tbsp\\.', ' c\\.', ' t\\b', ' tsp\\b', ' T\\b', ' tbl\\b', ' tbs\\b', ' tbsp\\b', ' c\\b']
>>> string_to_check = 'this is a test'
>>> for measurement in measurements:
    if re.search(measurement, string_to_check):
         print(measurement)


>>>

I had done two things here.

• [' ' + x + '\\.' for x in measurements] [' ' + x + '\\.' for x in measurements] , escape the dot in-order to match a literal dot, since dot is a special meta character in regex which matches any character.

• [' ' + x + r'\\b' for x in measurements] add word boundary \\b , since \\b matches between a word character and a non-word character, it won't pick spacet from <space>test

Answer 2

The problem is that you're coded for a different meaning of 'nothing behind it' than you're thinking of.

You've included the string ' t' in your array which is a substring of the string 'this is a test' [namely, it's sitting there at the front of the word test].

If you want 'nothing behind it' to mean 'at the end of the string' then you'll have to check what's at the end of the string instead of using substring search.

Answer 3

measurements
[' t ', ' tsp ', ' T ', ' tbl ', ' tbs ', ' tbsp ', ' c ', ' t.', ' tsp.', ' T.', ' tbl.', ' tbs.', ' tbsp.', ' c.', ' t', ' tsp', ' T', ' tbl', ' tbs', ' tbsp', ' c']

You can find ' t' in measurements.So ' t' in your check string "this is a[ t]est".
so, it's right to return ' t'.

if you want to exactly match ' t' not ' txxx', you need to
[' ' + x + r'\\b' for x in measurements]

Answer 4

A possible non-regex approach is to split string_to_check into a list of words. Then in will look for a word that matches exactly.

measurements = ['t', 'tsp', 'T', 'tbl', 'tbs', 'tbsp', 'c']

string_to_check = 'this is a test'
words_to_check = string_to_check.replace('.', ' ').split()
for measurement in measurements:
    if measurement in words_to_check:
        print(measurement)