如何删除文件中不包含数字的行？

Question

I have a file containing lines that look like this:

43
763
hello
4903
world

2632
hello 382

I need to strip every line which doesn't contain a number. That means the line can stay if it contains a string but only if it also contains any number.

The output would be:

43
763
4903
2632
hello 382

edit: So now I've got

with open('numstest.txt') as oldfile, open('numtest2.txt', 'w') as newfile:
    for line in oldfile:
        if not line.isalpha():
            newfile.write(line)

But for some reason, it's outputting the file exactly the same.

Answer 1

Just use a regular expression as follows

s = """43
       763
       hello
       4903
       world

       2632
       hello 382"""

p = re.compile(r"\d")
lines = (line for line in s.splitlines() if p.search(line))
for line in lines:
    print(line)
43
763
4903
2632
hello 382

See if it works for you.

Answer 2

Add all your strings to a list and print only the correct strings using the isalpha() method.

ls = ["43","763","hello","4903","world","2632","hello 382"]
for i in ls:
    if not i.isalpha():
        print(i)

EDIT : To get the file IO right, strip the newline character from a line before you check, so something like this:

with open('numstest.txt') as oldfile, open('numtest2.txt', 'w') as newfile:
    for line in oldfile:
        if not line.strip().isalpha():
            newfile.write(line)

The strip method removes the whitespace characters from both ends of a string so that you get the string "hello" for example, instead of "hello\\n"