使用python搜索文本文件中的行

Question

I am trying to search string in a txt file. Here is a sample txt file. I am working with:

abc
def
ghi
centre
jkl
mno
pqr
123
456

I am trying to match the lines in the file and if a match is found then exit the program if a match is not found then add the line to the file:

I have the following code that I am working with: my issue is it works correctly if I try to match "abc" in the file, but say if I try to match "pqr" I see my second if block is also executed.

Following is the code I have so far.

#!/usr/bin/python

new_data = raw_input("Enter txt:")    
file_name = "test.txt"

with open(file_name, "r") as F:
    data = F.readlines()

for num, line in enumerate(data, start=1):
    if line.strip() == new_data:
        print "exists {} {}".format(new_data, num)
        break

    if line.strip() != new_data:
        print "new data {} to be entered into line {}".format(new_data, num)

     else:
         print "break"

Following is the output i get if i try to match say "123" from the file:

Enter txt:123
new data 123 to be entered into line 1
new data 123 to be entered into line 2
new data 123 to be entered into line 3
new data 123 to be entered into line 4
new data 123 to be entered into line 5
new data 123 to be entered into line 6
new data 123 to be entered into line 7
exists 123 8

Answer 1

IIUC, you want the second block to execute only if the data does not exist. Well, try this:

for num, line in enumerate(data, start=1):
    if line.strip() == new_data:
        print "exists {} {}".format(new_data, num)
        break
else:
    print "new data {} to be entered into line {}".format(new_data, num)

You can take advantage of the for...else syntax. The else is executed if the loop does not break , ie, if the data does not exist in the file.

Answer 2

The problem with your code is that if the new_data is not found in iteration your 2nd if condition prints new data to be entered even if it exists in the subsequent iteration, only the the first data abc will give desired result as the iteration starts from there.

One good solution is already given by @COLDSPEED .

Another basic approach could be this:

for num, line in enumerate(data, start=1):
    if line.strip() == new_data:
        flag = 1
        print("exists {} {}".format(new_data, num))
        break
    else:
        flag = 0

if flag == 0:
    print("new data {} to be entered into line {}".format(new_data, num))

It will iterate through the whole data and if the new_data is found it will set the flag to be 1 and will break, else it will set the flag to be 0 and will print new data to be entered

Hope this help :)