On 11Nov2020 21:26, Karen Shaeffer <[email protected]> wrote:
>import io
>
>with io.open(filename, ‘r’) as fd:
> lines = fd.readlines(hint=1000)
> for line in lines:
> # do something
>
>
>I was just looking at the io module. io.open(‘file’, ‘r') returns an
>io.TextIOWrapper object, which has the io.TextIOWrapper.readlines(hint=-1/)
>method.
>
>
>>>> help(io.TextIOWrapper.readlines)
>readlines(self, hint=-1, /)
> Return a list of lines from the stream.
>
> hint can be specified to control the number of lines read: no more
> lines will be read if the total size (in bytes/characters) of all
> lines so far exceeds hint.
>
>I haven’t verified this, but that looks like it isn’t reading the entire file.
>With hint=1000, the method returns as many complete lines that consume less
>than 1000 bytes of the stream. I’m lazy. Didn’t test it. Seems like only 1000
>bytes would be read from the file, rather than the entire file?
Test it. To my eye, I also think that is what it means.
>The builtin ‘open’ function is defined in the io streams module. I presume the
>builtin open(‘file’, ‘r’) returns an io.TextIOWrapper object.
Test it:
>>> open('/dev/null','r')
<_io.TextIOWrapper name='/dev/null' mode='r' encoding='UTF-8'>
> And maybe the readlines method just isn’t documented?
It is documented though.
The docs for io.TextIOWrapper start with this (from the 3.8.0 docs I
have handy):
A buffered text stream over a BufferedIOBase binary stream. It
inherits TextIOBase.
The docs for io.TextIOBase start with this:
Base class for text streams. This class provides a character and
line based interface to stream I/O. It inherits IOBase.
And the docs for IOBase has the readlines method with the signature you
describe from its help.
Nte that if I look at the readlines from TextIOWrapper it says:
>>> open('/dev/null','r').readlines
<built-in method readlines of _io.TextIOWrapper object at 0x10b90ae10>
which probably means TextIOWrapper is a C implementation (for
performance), not doing the plain old class inheritance you'd get from a
pure Python implementation.
Cheers,
Cameron Simpson <[email protected]>
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