Python:记录类型错误:字符串格式化期间并非所有参数都转换

Question

这就是我正在做的事情

>>> import logging
>>> logging.getLogger().setLevel(logging.INFO)
>>> from datetime import date
>>> date = date.today()
>>> logging.info('date={}', date)
Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 846, in emit
    msg = self.format(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 723, in format
    return fmt.format(record)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 464, in format
    record.message = record.getMessage()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/logging/__init__.py", line 328, in getMessage
    msg = msg % self.args
TypeError: not all arguments converted during string formatting
Logged from file <stdin>, line 1
>>> 

我的python版本是

$ python --version
Python 2.7.3

如何让它发挥作用？

Answer 1

使用日志模块时不能使用新式格式；使用 %s 而不是 {}。

logging.info('date=%s', date)

日志模块使用旧式 % 运算符来格式化日志字符串。见 debug method了解更多详情。

如果您真的想使用 str.format() 字符串格式，请考虑在实际转换为字符串时使用应用格式“延迟”的自定义对象:

class BraceMessage(object):
    def __init__(self, fmt, *args, **kwargs):
        self.fmt = fmt
        self.args = args
        self.kwargs = kwargs

    def __str__(self):
        return self.fmt.format(*self.args, **self.kwargs)

__ = BraceMessage

logging.info(__('date={}', date))

这是一种方法 Python 3 logging module documentation proposes ，而且它恰好也适用于 Python 2。