使用带有输入功能的python中带引号和不带引号的模式搜索的差异

Question

What and why it makes diffrence while using Patt_Search as re.search(Patt_Search, line) then it works and re.search('Patt_Search', line) don't work , as i ran it and did not seen any error though.. it simply gets out..

Saying that, it works without the quote and don't work with quotes '' .

The way it works as Below:

$ cat Search_string_input.py
#!/usr/bin/python3
import re
File = input("Please Enter the File Name : ")
Patt_Search = input("Please Enter the Pattern you want to search : ")
ldap = open(File, mode='rt', encoding='utf-8')
for line in ldap:
    line = line.rstrip()
    #if re.search('12:00:16', line) :
    if re.search(Patt_Search, line) :
        print(line)

It works as below:

$ ./Search_string_input.py
Please Enter the File Name : ldap_data
Please Enter the Pattren you want to serach : 12:00:16
Jan 31 12:00:16 test-1 automount[3432]: bind_ldap_simple: lookup(ldap): Unable to bind to the LDAP server: (default), error Can't contact LDAP server
Jan 31 12:00:16 test-2 automount[3544]: bind_ldap_simple: lookup(ldap): Unable to bind to the LDAP server: (default), error Can't contact LDAP server
Jan 31 12:00:16 hsv-ch02 automount[3006]: bind_ldap_simple: lookup(ldap): Unable to bind to the LDAP server: (default), error Can't contact LDAP server

The way it don't works as Below:

$ cat Search_string_input.py
#!/usr/bin/python3
import re
File = input("Please Enter the File Name : ")
Patt_Search = input("Please Enter the Pattern you want to search : ")
ldap = open(File, mode='rt', encoding='utf-8')
for line in ldap:
    line = line.rstrip()
    #if re.search('12:00:16', line) :
    if re.search('Patt_Search', line) :
        print(line)

Result is as below, which don't yeild any output and no error though!

$ ./Search_string_input.py
Please Enter the File Name : ldap_data
Please Enter the Pattren you want to serach : 06:10:13

Answer 1

If you're using 'Patt_Search' , it just searches for the string literal 'Patt_Search' . A string containing a variable name has nothing to do with the variable itself.

Answer 2

• in the first case you're passing your input 12:00:16 , which is found three times in the file and printed to the screen.

• in the second case you're searching for the string Patt_Search , which can't be found in the file ldap_data , thus nothing gets printed to the screen.

https://docs.python.org/3/library/re.html

Answer 3

What is the purpose of this question? The first script apparently works as expected, so why not just use that?

In the second script, 'Patt_Search' is a literal string, so re.search('Patt_Search', line) searches for the string Patt_Search in the input line. I'm guessing that your LDAP data file does not contain the string Patt_Search anywhere, hence there will not be any matches, and there will be no output nor any errors.