Formatting dict keys: AttributeError: 'dict' object has no attribute 'keys()'

Question

在字符串中格式化字典键的正确方法是什么？

当我这样做时：

>>> foo = {'one key': 'one value', 'second key': 'second value'}
>>> "In the middle of a string: {foo.keys()}".format(**locals())

我的期望：

"In the middle of a string: ['one key', 'second key']"

我得到的：

Traceback (most recent call last):
  File "<pyshell#4>", line 1, in <module>
    "In the middle of a string: {foo.keys()}".format(**locals())
AttributeError: 'dict' object has no attribute 'keys()'

但是如你所见，我的字典有键：

>>> foo.keys()
['second key', 'one key']

Answer 1

您不能在占位符中调用方法。您可以访问属性和特性，甚至可以索引值 - 但您不能调用方法：

class Fun(object):
    def __init__(self, vals):
        self.vals = vals

    @property
    def keys_prop(self):
        return list(self.vals.keys())

    def keys_meth(self):
        return list(self.vals.keys())

方法示例（失败）：

>>> foo = Fun({'one key': 'one value', 'second key': 'second value'})
>>> "In the middle of a string: {foo.keys_meth()}".format(foo=foo)
AttributeError: 'Fun' object has no attribute 'keys_meth()'

属性示例（有效）：

>>> foo = Fun({'one key': 'one value', 'second key': 'second value'})
>>> "In the middle of a string: {foo.keys_prop}".format(foo=foo)
"In the middle of a string: ['one key', 'second key']"

格式语法清楚地表明您只能访问属性（la getattr）或索引（la __getitem__）占位符（取自 "Format String Syntax"）：

The arg_name can be followed by any number of index or attribute expressions. An expression of the form '.name' selects the named attribute using getattr(), while an expression of the form '[index]' does an index lookup using __getitem__().

使用 Python 3.6 你可以很容易地用 f-strings 做到这一点，你甚至不必传入 locals:

>>> foo = {'one key': 'one value', 'second key': 'second value'}
>>> f"In the middle of a string: {foo.keys()}"
"In the middle of a string: dict_keys(['one key', 'second key'])"

>>> foo = {'one key': 'one value', 'second key': 'second value'}
>>> f"In the middle of a string: {list(foo.keys())}"
"In the middle of a string: ['one key', 'second key']"

Answer 2

"In the middle of a string: {}".format(list(foo.keys()))

Answer 3

"In the middle of a string: {}".format([k for k in foo])

Answer 4

正如上面其他人所说，您无法按照自己喜欢的方式进行操作，这里有一些额外的信息需要遵循python string format calling a function

Formatting dict keys: AttributeError: 'dict' object has no attribute 'keys()'

Formatting dict keys: AttributeError: 'dict' object has no attribute 'keys()'

python

methods

dictionary

string-formatting

attributeerror