From 4208321a199f29cec8fd2aa07f137edd07056177 Mon Sep 17 00:00:00 2001 From: Mark Pilgrim Date: Thu, 16 Jul 2009 08:53:24 -0400 Subject: [PATCH] notes about xreadlines() --- porting-code-to-python-3-with-2to3.html | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/porting-code-to-python-3-with-2to3.html b/porting-code-to-python-3-with-2to3.html index 8f98b49..108e74c 100644 --- a/porting-code-to-python-3-with-2to3.html +++ b/porting-code-to-python-3-with-2to3.html @@ -880,6 +880,8 @@ except:

In Python 2, file objects had an xreadlines() method which returned an iterator that would read the file one line at a time. This was useful in for loops, among other places. In fact, it was so useful, later versions of Python 2 added the capability to file objects themselves. +

In Python 3, the xreadlines() method no longer exists. 2to3 can fix the simple cases, but some edge cases will require manual intervention. +
Notes Python 2 @@ -889,12 +891,12 @@ except: for line in a_file:
② for line in a_file.xreadlines(5): -no change +no change (broken)

  1. If you used to call xreadlines() with no arguments, 2to3 will convert it to just the file object. In Python 3, this will accomplish the same thing: read the file one line at a time and execute the body of the for loop. -
  2. If you used to call xreadlines() with an argument (the number of lines to read at a time), keep doing that. It still works in Python 3, and 2to3 will not change it. +
  3. If you used to call xreadlines() with an argument (the number of lines to read at a time), 2to3 will not fix it, and your code will fail with an AttributeError: '_io.TextIOWrapper' object has no attribute 'xreadlines'. You can manually change xreadlines() to readlines() to get it to work in Python 3. (The readlines() method now returns an iterator, so it is just as efficient as xreadlines() was in Python 2.)

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