Python2.7与Python3.5中ConfigParser处理重复section的差异及疑问

Great questions—this is a common point of confusion when moving between Python 2 and 3's config handling. Let's unpack each one:

1. Is Python 2.7's ConfigParser behavior (allowing duplicate sections) a bug? #

Short answer: No, it's not a bug—it was an intentional design choice for Python 2's ConfigParser.

Back when Python 2's ConfigParser was developed, the library was built with a "forgiving" approach to INI files. The documentation explicitly stated that duplicate sections would have their key-value pairs merged, with later entries overriding earlier ones for duplicate keys. This was meant to handle cases where legacy systems or tools might generate INI files with repeated sections (even though that's not strictly compliant with typical INI file conventions).

Your expectation of an exception is totally reasonable given Python 3's stricter defaults, but in Python 2's context, this behavior was working as intended.

2. Is "reading the latest value and merging previous options" the correct behavior? #

This depends on your perspective:

• From a compatibility standpoint: If you're working with legacy systems that produce INI files with duplicate sections, this behavior is useful—it lets you parse the file without errors and get a combined set of config options (with later values taking precedence).
• From a config correctness standpoint: No, this isn't ideal. Standard INI file conventions don't allow duplicate sections, and having them usually indicates a mistake (like a typo or accidental duplication in the config file). Python 3's default strict=True behavior is safer here because it catches these errors early, preventing unexpected config values from slipping through.

To illustrate, here's how Python 2 handles it:

from ConfigParser import ConfigParser

config = ConfigParser()
# Sample INI content:
# [my_section]
# key1 = old_val
# [my_section]
# key1 = new_val
# key2 = extra_val
config.read('duplicate_config.ini')

print(config.get('my_section', 'key1'))  # Outputs 'new_val' (latest value)
print(config.get('my_section', 'key2'))  # Outputs 'extra_val' (merged from later section)

And Python 3's default strict behavior:

from configparser import ConfigParser

config = ConfigParser()  # strict=True is default in Python 3.2+
try:
    config.read('duplicate_config.ini')
except ValueError as e:
    print(e)  # Raises: "section 'my_section' already exists"

Wrap-up #

Python 2's behavior was a pragmatic choice for its era, but Python 3's stricter default aligns better with modern expectations of config file validity.

内容的提问来源于stack exchange，提问作者Alex