Python中有字典解读吗? (函数返回的问题) [英] Are there dictionary comprehensions in Python? (Problem with function returning dict)
问题描述
预期输出:
我知道列表推理,字典理解怎么样? >>> countChar('google')
{'e':1,'g':2,'l':1,'o':2}
>>> countLetters('apple')
{'a':1,'e':1,'l':1,'p':2}
>>> countLetters('')
{}
代码(我是初学者):
def countChar(word):
l = []
#从单词
for c in word:l.append(c)
sortedList = sorted(l)
uniqueSet = set(sortedList)
return {item:word.count(item)for unique in uniqueSet}
此代码有什么问题?为什么我得到这个 SyntaxError
?
return {item:word.count(item)for unique in uniqueSet}
^
SyntaxError:无效语法
编辑正如agf在评论中指出的,另一个答案是Python 2.7或更新版本的字典理解。
def countChar(word ):
return set((item,word.count(item))for set in(())
>>>> countChar('google')
{'e':1,'g':2,'o':2,'l':1}
>>> countChar('apple')
{'a':1,'p':2,'e':1,'l':1}
没有必要将单词
转换为列表或将其排序,然后将其转换为集合,因为字符串是可迭代的:
>>> set('google')
set(['e','o','g','l'])
对于Python 2.6及以下版本,没有字典理解,这可能是您看到语法错误的原因。替代方法是使用理解或生成器创建一个键值元组列表,并将其传递到 dict()
内置。
I know about list comprehensions, what about dictionary comprehensions?
Expected Output:
>>> countChar('google')
{'e': 1, 'g': 2, 'l': 1, 'o': 2}
>>> countLetters('apple')
{'a': 1, 'e': 1, 'l': 1, 'p': 2}
>>> countLetters('')
{}
Code (I'm a beginner):
def countChar(word):
l = []
#get a list from word
for c in word: l.append(c)
sortedList = sorted(l)
uniqueSet = set(sortedList)
return {item:word.count(item) for item in uniqueSet }
What is the problem with this code? Why do I get this SyntaxError
?
return { item:word.count(item) for item in uniqueSet }
^
SyntaxError: invalid syntax
edit: As agf pointed out in comments and the other answer, there is a dictionary comprehension for Python 2.7 or newer.
def countChar(word):
return dict((item, word.count(item)) for item in set(word))
>>> countChar('google')
{'e': 1, 'g': 2, 'o': 2, 'l': 1}
>>> countChar('apple')
{'a': 1, 'p': 2, 'e': 1, 'l': 1}
There is no need to convert word
to a list or sort it before turning it into a set since strings are iterable:
>>> set('google')
set(['e', 'o', 'g', 'l'])
There is no dictionary comprehension with for Python 2.6 and below, which could be why you are seeing the syntax error. The alternative is to create a list of key-value tuples using a comprehension or generator and passing that into the dict()
built-in.
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