why is_file_like needs to see __iter__

[stonefly]

I have a question regarding the new is_file_like function and its usage in IO functions like read_csv

This new change in pandas 0.20 breaks many codes which previously assume that a file-like object is just an object possessing read or write method.

Is there any specific reason we have to enforce such conditions?

When making such changes why we have to break the previous behaviors?

[jorisvandenbossche]

@stonefly There are a couple of related issues about this, eg see #17135, #16135, #16530
Can you see if you have additional issues that are not mentioned there?

If so, please be more specific: what files are giving trouble? What version of pandas are you using? (some things were fixed only in 0.20.2)

[stonefly]

Hi, I can confirm that 0.20.2 fixes our problem (because it does not see next method in 0.20.1).

But in general it is not the first time we got surprising breaks due to some changes like this.

Do you know why we start changing this logic since 0.20?

Isn't duck-typing rule sufficient here?

[jreback]

closing as this is duplicated by many issues.