right usage of __repr__() in python?

Question

I have a container class which I would like to use to print all the elements in it.

I'd like to print them to file or console.

I've laid out the element (Patch) and container class as below and __repr__(self).
I'm not sure I understood the purpose of __repr__() and am wondering whether the usage here is OK.

class Patch:
    def __init__(self, folder_name, file_name):
        self.folder_name = folder_name
        self.file_name = file_name
        self.full_path = os.path.join(self.folder_name, self.file_name)
        self.file_hash = md5_for_file(open(self.full_path, 'r'))
        self.file_size = os.path.getsize(self.full_path)

    def __repr__(self):
        return "%s %s %s" % (self.file_name, self.file_hash, self.file_size)

class PatchContainer:
    def __init__(self):
        self.patch_folder_dict = collections.OrderedDict()
        self.patch_file_set = set()
    def addPatch(self, patch):
        if patch.file_name in self.patch_file_set:
            print '*** Delete the file ', patch.full_path, ' ***'
            return
        self.patch_file_set.add(patch.file_name)
        if not patch.folder_name in self.patch_folder_dict:
            self.patch_folder_dict[patch.folder_name] = [patch]
        else:
            self.patch_folder_dict[patch.folder_name].append(patch)

    def prettyPrint(self, writeable_object=PATCH_META_FILE):
        sys.stdout = writeable_object
        for patch_folder in self.patch_folder_dict.keys():
            print patch_folder
            patch_list = self.patch_folder_dict[patch_folder]
            for patch in patch_list:
                print patch
        sys.stdout = sys.__stdout__

It works as intended but please comment on whether the style/usage are fine.

Answer 1

This looks like you probably want __str__. They are similar, but __str__ returns something intended for human consumption; __repr__ should return something intended for Python consumption - it should either be a Python expression that will evaluate to an equal object, or something in angle brackets like the default <classname object at id>. See the documentation for the builtin repr(object), which ends up calling object.__repr__():

For many types, this function makes an attempt to return a string that would yield an object with the same value when passed to eval(), otherwise the representation is a string enclosed in angle brackets that contains the name of the type of the object together with additional information

Answer 2

It's a human-readable representation of the object.

• "Purpose of Python's __repr__": clicky
• "Difference between __str__ and __repr__ in Python": clicky
• Python documentation: clicky