Python:尝试除了 KeyError 与 if has_key()

Question

这个问题在这里已经有了答案:

`if key in dict` vs. `try/except` - which is more readable idiom? (11 个回答)

关闭 6年前。

在下面的代码中，什么更高效/更“Pythonic”？使用 try-catch 子句还是 if-else 子句？

fname = 'AdobeARM.log'

letters = {}

with open(fname,'r') as f:
    for line in f:
        for c in line:
            try:
                letters[c] += 1
            except KeyError:
                letters[c] = 1

print letters

VS.

fname = 'AdobeARM.log'

letters = {}

with open(fname,'r') as f:
    for line in f:
        for c in line:
            if letters.has_key(c):
                letters[c] += 1
            else:
                letters[c] = 1

print letters

我倾向于使用 try catch 选项，但我不确定为什么。

Answer 1

使用 dict.get() :

get(key[, default])

Return the value for key if key is in the dictionary, else default. If default is not given, it defaults to None, so that this method never raises a KeyError.

换句话说d.get('x', c)相当于 d['x'] if 'x' in d else c .

示例:

In [24]: d = {'a':1, 'b':2}

In [27]: d['d'] = d.get('d', 0) + 1  # 0 is the default value

In [28]: d
Out[28]: {'a': 1, 'b': 2, 'd': 1}

In [29]: d['d'] = d.get('d', 0) + 1

In [30]: d
Out[30]: {'a': 1, 'b': 2, 'd': 2}