Go to a specific line in Python?

Question

I want to go to line 34 in a.txt file and read it. How would you do that in Python?

Answer 1

Use Python Standard Library's linecache module:

line = linecache.getline(thefilename, 33)

should do exactly what you want. You don't even need to open the file -- linecache does it all for you!

Answer 2

This code will open the file, read the line and print it.

# Open and read file into buffer
f = open(file,"r")
lines = f.readlines()

# If we need to read line 33, and assign it to some variable
x = lines[33]
print(x)

Answer 3

A solution that will not read more of the file than necessary is

from itertools import islice
line_number = 34

with open(filename) as f:
    # Adjust index since Python/islice indexes from 0 and the first 
    # line of a file is line 1
    line = next(islice(f, line_number - 1, line_number))

A very straightforward solution is

line_number = 34

with open(filename) as f:
    f.readlines()[line_number - 1]

Answer 4

There's two ways:

1. Read the file, line by line, stop when you've gotten to the line you want
2. Use f.readlines() which will read the entire file into memory, and return it as a list of lines, then extract the 34th item from that list.

Solution 1

Benefit: You only keep, in memory, the specific line you want.

code:

for i in xrange(34):
    line = f.readline();
# when you get here, line will be the 34th line, or None, if there wasn't
# enough lines in the file

Solution 2

Benefit: Much less code
Downside: Reads the entire file into memory
Problem: Will crash if less than 34 elements are present in the list, needs error handling

line = f.readlines()[33]

Answer 5

您可以阅读所有行并在以后索引该行。

line = open('filename').readlines()[33]

Answer 6

for linenum,line in enumerate(open("file")):
    if linenum+1==34: print line.rstrip()

Answer 7

I made a thread about this and didn't receive help so I took matter into my own hands.

Not any complicated code here.

import linecache
#Simply just importing the linecache function to read our line of choosing

number = int(input("Enter a number from 1-10 for a random quote "))
#Asks the user for which number they would like to read(not necessary) 

lines = linecache.getline("Quotes.txt", number)
#Create a new variable in order to grab the specific line, the variable 
#integer can be replaced by any integer of your choosing.

print(lines)
#This will print the line of your choosing.

If you are completing this in python make sure you have both files (.py) and (.txt) in the same location otherwise python will not be able to retrieve this, unless you specify the file location. EG.

linecache.getline("C:/Directory/Folder/Quotes.txt

This is used when the file is in another folder than the .py file you are using.

Hope this helps!

Answer 8

Option that always closes the file and doesn't load the whole file into memory

with open('file.txt') as f:
    for i, line in enumerate(f):
        if i+1 == 34: break
    print(line.rstrip())