使用单词列表的正则表达式

Question

I'm using Python.

I have some strings :

'1 banana', '100 g of sugar', '1 cup of flour'

I need to distinguish the food from the quantity. I have an array of quantities type

quantities = ['g', 'cup', 'kg', 'L'] altern = '|'.join(quantities)

and so with using a regular expression I would like to get for example for '1 cup of flour' : 'flour' and '1 cup of' , for '1 banana' : '1' and 'banana'

I have written this regexp to match the quantity part of the strings above :

\d{1,3}\s<altern>?\s?(\bof\b)?

but I'm very unsure about this ...particularly on how to introduce the altern variable in the regular expression.

Answer 1

I think your amounts are units , so I took the liberty to fix this misnomer. I propose to use named grouping to ease understanding the output.

import re

units = [ 'g', 'cup', 'kg', 'L' ]
anyUnitRE = '|'.join(units)

inputs = [ '1 banana', '100 g of sugar', '1 cup of flour' ]

for input in inputs:
  m = re.match(
    r'(?P<amount>\d{1,3})\s*'
    r'(?P<unit>(' + anyUnitRE + r')?)\s*'
    r'(?P<preposition>(of)?)\s*'
    r'(?P<name>.*)', input)
  print m and m.groupdict()

The output will be sth like this:

{'preposition': '', 'amount': '1', 'name': 'banana', 'unit': ''}
{'preposition': 'of', 'amount': '100', 'name': 'sugar', 'unit': 'g'}
{'preposition': 'of', 'amount': '1', 'name': 'flour', 'unit': 'cup'}

So you can do sth like this:

if m.groupdict()['name'] == 'sugar':
  …
amount = int(m.groupdict()['amount'])
unit = m.groupdict()['unit']

Answer 2

I think you can use this:

"(.*?) (\w*)$"

And get \\1 for first part and \\2 for second part.

[Regex Demo]

And for a better regex:

"^((?=.*of)((.*of)(.*)))|((?!.*of)(\d+)(.*))$"

And get \\3 and \\6 for first part and \\4 and \\7 for second part.

Answer 3

You can try this code:

import re
lst = ['1 banana', '100 g of sugar', '1 cup of flour']
quantities = ['g', 'cup', 'kg', 'L']
altern = '|'.join(quantities)
r = r'(\d{1,3})\s*((?:%s)?s?(?:\s*\bof\b)?\s*\S+)'%(altern)
for x in lst:
    print re.findall(r, x)

See demo

Output:

[('1', 'banana')]
[('100', 'g of sugar')]
[('1', 'cup of flour')]

Answer 4

Why do you want to do this with regular expressions? You can use Python's string splitting functions instead:

def qsplit(a):
    """Return a tuple of quantity and ingredient"""

    if not a:
        return None

    if not a[0] in "0123456789":
        return ["0", a]

    if " of " in a:
        return a.split(" of ", 1)

    return a.split(None, 1)