Regex exact match

Question:

I have the following sentence:
"The size of the lunch box is around 1.5l or 1500ml"

How can I change this to:
"The size of the lunch box is around 1.5 liter or 1500 milliliter"

In some cases, the value might also be present as "1.5 l or 1500 ml" with a space.

I am not be able to capture the "l" or "ml" when I am trying to build a function, or it is giving me an escape error.

I tried:

def stnd(text):

text = re.sub('^l%',' liter', text) 
text = re.sub('^ml%',' milliliter', text) 

text = re.sub('^d+.d+s*l$','^d+.d+s*liter$', text) 
text = re.sub('^^d+.d+s*ml$%','^d+.d+s*milliliter$', text) 

return text
Asked By: C C

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Source

Answers:

We can handle this replacement using a dictionary of lookup values and replacements.

d = {"l": "liter", "ml": "milliliter"}
inp = "The size of the lunch box is around 1.5l or 1500ml"
output = re.sub(r'(d+(?:.d+)?)s*(ml|l)', lambda m: m.group(1) + " " + d[m.group(2)], inp)
print(output)

# The size of the lunch box is around 1.5 liter or 1500 milliliter

def stnd(text):
    return re.sub(r'(d+(?:.d+)?)s*(m?l)', lambda m: m.group(1) + " " + d[m.group(2)], text)
Answered By: Tim Biegeleisen

You could use a dict to list all the units as the key, and use a pattern to find a digit followed by either ml or l which you could then use as the key for the dict to get the value.

(?<=d)m?lb

The pattern matches:

  • (?<=d) Positive lookbehind, assert a digit to the left
  • m?lb Match an optional m followed by b and a word boundary

See a regex demo.

Example

s = "The size of the lunch box is around 1.5l or 1500ml"
pattern = r"(?<=d)m?lb"
dct = {
    "ml": "milliliter",
    "l": "liter"
}
result = re.sub(pattern, lambda x: " " + dct[x.group()] if x.group() in dct else x, s)
print(result)

Output

The size of the lunch box is around 1.5 liter or 1500 milliliter
Answered By: The fourth bird