Reports

As I can't post this in a comment …
I get a strange comportment :\

>>> with open("./Python/nombres_premiers", "r") as f:
...     a = f.seek(0,2)
...     l = ""
...     for i in range(a-2,0,-1):
...        f.seek(i)
...        l = f.readline() + l
...        if l[0]=="\n":
...           break
... 
1023648626
1023648625
1023648624
1023648623
1023648622
1023648621
1023648620
1023648619
1023648618
1023648617
1023648616
>>> l
'\n2001098251\n001098251\n01098251\n1098251\n098251\n98251\n8251\n251\n51\n1\n'
>>> with open("./Python/nombres_premiers", "r") as f:
...     a = f.seek(0,2)
...     l = ""
...     for i in range(a-2,0,-1):
...        f.seek(i)
...        l = f.readline()
...        if l[0]=="\n":
...           break
... 
1023648626
1023648625
1023648624
1023648623
1023648622
1023648621
1023648620
1023648619
1023648618
1023648617
1023648616
>>> l
'\n'

How to get l = 2001098251 ?

79259767