从文本文件中读取行，如果特定单词 == 100，则打印该行

Question

I have a text file that i want to read using python. The text file contains words and a value such as (rt= 3.878). I want to write a script using python to read the text file and if rt in line is == 3.878, print that line. I managed to write this piece of code so far.

    with open ('/home/Desktop/hello.txt', 'r') as f:
             f.readline()
             for line in f:
                     if 'rt' in line == 3.878
                              print(line)

This code returns nothing. Could anyone kindly point out what I might be doing wrong? thanks in advance!

Answer 1

Apart from the syntax error of missing : , if 'rt' in line == 3.878 is a bug. The in operator checks membership and returns True or False , which are 1 and 0 respective in int context. So == will produce unexpected result.

Anyway, things won't happen magically just because we want them to. Some processing need to be done. If n is the number you want to match and assuming the lines are like number = 1.234

if line.split("=")[-1].strip() == str(n): # don't float() the left side
    # do something

Answer 2

As your file appears to have a very regular format, you could turn it into a dictionary:

with open('/home/Desktop/hello.txt') as f:
    result = {k:float(v) for k,v in (line.split('=') for line in f)}

Then directly access the key you're interested in and check its value:

if result.get('rt') == 3.878:
    print('rt=3.878')

You can quickly look up any key and its corresponding value without having to iterate through the whole file (or a saved sequence like a list ) again.

If your file can have multiple lines with the same key, you'll need to group their values into a list , as dictionaries can't have duplicate keys. The common way to do this is with collections.defaultdict :

import collections.defaultdict as dd
result = dd(list)
with open('/home/Desktop/hello.txt') as f:
    for line in f:
        k,v = line.split('=')
        result[k].append(float(v)

You can then quickly look up any key and its corresponding values like you could with the basic dictionary. For example, you could print all values above a certain limit for a given key:

print(*(v for v in sorted(result.get('rt', '')) if v>100), sep='\n')

If you're really only interested in the rt key and in checking that it has a value of 3.878 , you could do that in a few ways.

First, simply reading the whole file:

with open('/home/Desktop/hello.txt') as f:
    print('rt=3.878' in f.read())

Iterating through the file and stopping when the desired value is reached:

with open('/home/Desktop/hello.txt') as f:
    for line in f:
        if line.strip() == 'rt=3.878':
            print(line)
            break

Eagerly evaluating the contents of the file and checking for the desired value in there:

with open('/home/Desktop/hello.txt') as f:
    print('rt=3.878' in {line.strip() for line in f})

Creating a dictionary is the most versatile approach, and the one I'd recommend. Iterating through the file and stopping when the desired value is reached is probably the best of the remaining approaches, as it will stop going through the file if and when it finds what you're looking for.

Note that you could also find this content by simply opening the file in a text editor and searching for rt=3.878 with Ctrl + F . The simple approach is often the best.

Answer 3

You can split each line on the = delimiter and then compare the second index of the result, after casting it from string to a float:

with open("file.txt", "r") as f:
    for line in f.readlines():
        if float(line.split("=")[1]) == 3.878:
            print line

This is what split on line looks like:

line = "rt=3.878"
print line.split("=")[0] # rt
print line.split("=")[1] # 3.878
print type(line.split("=")[1]) # type 'str'
print type(float(line.split("=")[1])) # type 'float'

Update Replace you loop with this to only consider lines where the first string is "rt" and not eg "ACCOUNT":

with open("file.txt", "r") as f:
    for line in f.readlines():
        if line.split("=")[0] == "rt":
            if float(line.split("=")[1]) == 3.878:
                print line

Answer 4

Well, may be:

with open ('/home/Desktop/hello.txt', 'r') as f:
         f.readline()
         for line in f:
                 if 'rt=3.878' in line:
                          print(line)