[fix] config ignore imported modules and functions

[SuTanTank]

Motivation

When use import like import os.path as osp in config. The parsed config's _cfg_dict contains an entry which looks like osp: <module .....

Then when calling pretty_text(), this dict is converted back to string, which is different from the original config., Then this string is formatted by yapf and error occurs.

# config: pretty_text()
        cfg_dict = self._cfg_dict.to_dict()
        text = _format_dict(cfg_dict, outest_level=True)
        # copied from setup.cfg
        yapf_style = dict(
            based_on_style='pep8',
            blank_line_before_nested_class_or_def=True,
            split_before_expression_after_opening_paren=True)
        text, _ = FormatCode(text, style_config=yapf_style, verify=True)

Modification

When parsing a config file to dict, modules and functions are ignored.

BC-breaking (Optional)

No

Use cases (Optional)

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with some of those projects, like MMDet or MMCls.
• CLA has been signed and all committers have signed the CLA in this PR.

[HAOCHENYE]

LGTM.

[ZwwWayne]

Hi @SuTanTank ,
Thanks for the kind PR. Would you like to also update the unit tests to test the updated code?

[SuTanTank]

What function should I test? There is no new API introduced.