What is exactly a file-like object in Python?

别说谁变了你拦得住时间么 提交于 2019-12-04 19:33:04


In http://docs.python.org/library/json.html:

simplejson.load(fp[, encoding[, cls[, object_hook[, parse_float[, parse_int[, parse_constant[, object_pairs_hook[, use_decimal[, **kw]]]]]]]]])

Deserialize fp (a .read()-supporting file-like object containing a JSON document) to a Python object.

I do know what read() and write() do.

But after reading this description "read()-supporting file-like object", I find I don't know what object type supports the read() and write().

And I can't find that in the rest of documentation. Anyone could elaborate more on the statement?

Why I ask this question is for getting "simplejson.load(urllib.open(...))" done.
The return value of "urllib.open(...)" is not a valid object, so I have to tailor it for simplejson. However, it seems like that string is not read()-supporting.


file-like objects are mainly StringIO objects, connected sockets and well.. actual file objects. If everything goes fine, urllib.urlopen() also returns a file-like objekt supporting the necessary methods.


simplejson has the calls loads and dumps that consumes and produce strings instead of file like objects.

This link has an example in the context of StringIO and simplejson for both file-like and string objects.



In Python, a file object is an object exposing an API having methods for performing operations typically done on files, such as read() or write().

In the question's example: simplejson.load(fp, ...), the object passed as fp is only required to have a read() method, callable in the same way as a read() on a file (i.e. accepting an optional parameter size and returning either a str or a bytes object).

This does not need to be a real file, though, as long as it has a read() method.

A file-like object is just a synonym for file-object. See Python Glossary.


From the glossary:

file-like object

A synonym for file object

and a file object is

file object

An object exposing a file-oriented API (with methods such as read() or write()) to an underlying resource. Depending on the way it was created, a file object can mediate access to a real on-disk file or to another type of storage or communication device (for example standard input/output, in-memory buffers, sockets, pipes, etc.). File objects are also called file-like objects or streams.

There are actually three categories of file objects: raw binary files, buffered binary files and text files. Their interfaces are defined in the io module. The canonical way to create a file object is by using the open() function.