python [regex] - 搜索 function 在从文件中读取行时不起作用

Question

I have written the following python section code in order to open a file and read it line by line and detect if a line is starting by a letter or number.

For some strange reason, the search() function is not working correct as a result we never enters the if statement. My code is below:

import re

path = "path/to/my/file/data.txt" 

with open(path, 'r') as f:
    line = f.read()
    if (re.search("^[a-zA-Z0-9]", line)):
        print "YES"

Answer 1

If you want to read the file line by line, you need to iterate over it, like this, f.read() will just load the entire file as a string, so your if will only be reached once for all data. If it doesn't start with an alphanumerical, you won't reach your print .

To iterate over it, you can do that with

with open(path, 'r') as f:
    for line in f:
        if (re.search("^[a-zA-Z0-9]", line)):
            print("YES")

Answer 2

To iterate over the file line by line

import re

path = "path/to/my/file/data.txt" 

with open(path, 'r') as f:
    for line in f:       # iterating over the file object line by line
        if (re.search("^[a-zA-Z0-9]", line)):
            print "YES"