格式化字典鍵：AttributeError：'字典'對象沒有屬性'keys（）'

Question

在字符串中格式化字典鍵的正確方法是什麼？

當我這樣做：

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

我想到：

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

我能得到什麼：

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()' 

但你可以看到，我的字典具有鍵：

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

Answer 1

您不能在佔位符中調用方法。您可以訪問特性和屬性，甚至指數的價值 - 但你不能調用方法：

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()) 

實例與方法（不及格）：

>>> 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()' 

實例財產（工作）：

>>> 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']" 

格式化語法表明您只能訪問屬性（a la getattr）或索引（a la __getitem__）佔位符（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，你可以輕鬆地與F-串做到這一點，你甚至不必在locals經過：

>>> 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

正如上面其他人所說的那樣，你不能按照你喜歡的方式去做，這裏有更多的信息可以參考python string format calling a function