It would be handy to be able to pass the `length` default argument defined by `shutil.copyfileobj()` to other public functions througout the module. When copying very large files (1GB +), increasing the memory buffer can divide the copy time in half and currently the only way to accomplish this is by overriding the needed function(s) which call `shutil.copyfileobj()`. I propose a simple non-invasive change where the following functions will also expose the `length` kwarg and pass it downwards to `copyfileobj`: - copyfile - copy - copy2
How about increasing default value to 32KiB or 64KiB too? binutils's cp works well for most cases, while it doesn't have option to specify blocksize. I want Python's copy functions works nice enough for common cases too. binutils cp uses 128KiB block for normal file. see more information in https://github.com/coreutils/coreutils/blob/master/src/ioblksize.h But copyfileobj can be used other file-likes. On Linux, typical socket buffer size is 128KiB, and typical pipe buffer size is 64KiB. So block size larger than 64KiB may cause unneeded blocking. That's why I suggested 32KiB or 64KiB.
