Question: i have a file with information in the pattern of:

```
.343423 1
.434322 1
.453434 1
.534342 1

```

Equal size each line and row in sorted order..I have a variable "a" with a value and need to get the row number which it closest to "a" comparing with the values in the 1st column..

Till now i was coping the 1st column element into list and then using bisect method i am getting the row\_num...but as i need to perform this many times..this has become painfully slow as i need to copy some 4000 element to list everytime..

so now i am thinking of doing it with dict instead of datastructure as i would be faster...but i dont know whether we can use dict in bisect if possible how can we use for this case please suggest...
if not possible are they any method for loading data into list faster then normal???
thanking you...

Answer: 
Here is a way to use `bisect` without reading the entire file. The OS will end up reading much more of the file than you need regardless, so you won't see a performance gain until `data.txt` big enough

```
from os import SEEK_END
from bisect import bisect

class ListProxy(object):
    def __init__(self, f):
        self.f = f
        self.line_len = len(f.readline())
        self.f.seek(0, SEEK_END)
        self.num_lines = self.f.tell()//self.line_len

    def __len__(self):
        return self.num_lines

    def __getitem__(self, idx):
        self.f.seek(idx*self.line_len)
        return float(self.f.read(7))

with open("data.txt") as f:
    lp = ListProxy(f)    
    num = .44
    idx = bisect(lp, num)
    if idx != 0 and num - lp[idx-1] < lp[idx] - num:
        idx -=1
    print num, idx

```
I don't get why you need to copy the elements. This is the slow part. Can't you load the list one time on startup, and then always use the same list ?

A dict will be slower than a list anyway (and I belive [not sure] it is implemented as a hash\_map, thus there is no order, thus you can't use bisect).