如何从字符串列表中删除特殊字符？

Question

I am reading a file and using a regex on the file content to perform some operations. While reading the file, I don't find any special characters in it but after using the regex on the file content and saving it to a list, there are special characters like \\t and \\xa0 before numbers.

Example file content:

Hydrochloric Acid to pHÂ 3.3-5.0        q.s.    q.s.    q.s.    pH-regulator    Ph Eur, NF

After applying regex becomes:

Hydrochloric Acid to pHÂ\xa03.3-5.0\tq.s.\tq.s.\tq.s.\tpH-regulator\tPh Eur, NF

How do I remove all these without individual string replacement techniques?

Code:

def extract(filename):
    file=open(filename)
    file=file.read()
    print(file)
    print("wefewwEF3RF3")
    result = []
    med = r"(?:{})".format("|".join(map(re.escape, medicines)))
    pattern = re.compile(r"^\s*" + med + r".*(?:\n[^\w\n]*\d*\.?\d+[^\w\n]*(?:\n.*){2})?", re.M|re.IGNORECASE)
    result = pattern.findall(file)
#    result.encode('ascii', 'ignore')
    newresult = []
    for line in result:
        newresult.append((line.strip()))
    return newresult

The newresult list contains all these special characters which are not present in the original file.

Answer 1

If you know all these special characters you can use maketrans and translate methods of str to replace them with spaces following way:

txt = 'Hydrochloric Acid to pHÂ\xa03.3-5.0\tq.s.\tq.s.\tq.s.\tpH-regulator\tPh Eur, NF'
t = ''.maketrans('\xa0\t','  ')
newtxt = txt.translate(t)
print(newtxt)

Output

Hydrochloric Acid to pHÂ 3.3-5.0 q.s. q.s. q.s. pH-regulator Ph Eur, NF

maketrans accept 2 or 3 arguments. It creates translation table, which then might be used in translate method and work as follows: every char from first argument of maketrans is replace with corresponding char from second argument of maketrans (thus they must have equal length) and every character present in third argument of maketrans is removed. In example above \\xa0 is replaced with space and \\t is replaced with space.

Answer 2

Hi,

Can you check your code under a different Python version? It seems to work without error on 3.8.0.

def extract(filename):
    file='Hydrochloric Acid to pHÂ 3.3-5.0        q.s.    q.s.    q.s.    pH-regulator    Ph Eur, NF'
    result = []
    med = r"(?:{})".format("|".join(map(re.escape, file)))
    pattern = re.compile(r"^\s*" + med + r".*(?:\n[^\w\n]*\d*\.?\d+[^\w\n]*(?:\n.*){2})?", re.M|re.IGNORECASE)
    result = pattern.findall(file)
    #result.encode('ascii', 'ignore')
    newresult = []
    for line in result:
        newresult.append((line.strip()))
    print(file)
    print (newresult)
    return newresult
extract('test')