read specific line in csv file , python

Question

In an CSV file with python we can read all the file line by line or row by row , I want to read specific line (line number 24 example ) without reading all the file and all the lines.

Melodramatic

possible duplicate of Start reading and writing on specific line on CSV with Python – Kyliekylila

Answer 1

You can use linecache.getline:

linecache.getline(filename, lineno[, module_globals])

Get line lineno from file named filename. This function will never raise an exception — it will return '' on errors (the terminating newline character will be included for lines that are found).

import linecache


line = linecache.getline("foo.csv",24)

Or use the consume recipe from itertools to move the pointer:

import collections
from itertools import islice

def consume(iterator, n):
    "Advance the iterator n-steps ahead. If n is none, consume entirely."
    # Use functions that consume iterators at C speed.
    if n is None:
        # feed the entire iterator into a zero-length deque
        collections.deque(iterator, maxlen=0)
    else:
        # advance to the empty slice starting at position n
        next(islice(iterator, n, n), None)

with open("foo.csv") as f:
    consume(f,23)
    line = next(f)

Kovach

@xtofl, a file object is its own iterator, when you for line in f:..., next is repeatedly called – Kovach

and to start the reading from a specific line and not from the beginning? it workwith simply consume(f,X) and increment the X each time (initialize the X on the desired position), thanks for your usefull answer :) – Melodramatic

@user3967257, use the consume recipe if you want to start from a certain line, the second arg to consume is the amount of lines to consume then just for line in f... to read the rest of the lines. – Kovach

this is what I mean for i in range(X,limit): consume(f,i) – Melodramatic

Answer 2

Alternatively you can leverage the nrows and skiprows argument in pandas

line_number = 30
pd.read_csv('big.csv.gz', sep = "\t", nrows = 1, skiprows = line_number - 1)

remember skiprows can be a list so if you need the header use

pd.read_csv('big.csv.gz', sep = "\t", nrows = 1, skiprows = list(range(1, line_number - 1)))

Sianna