Python字符串神奇地转换为元组。 为什么？

Question

I've got a dict in which I load some info, among others a name which is a plain string. But somehow, when I assign it to a key in the dict it gets converted to a tuple, and I have no idea why.

Here's some of my code:

sentTo = str(sentTo)
print type(sentTo), sentTo
ticketJson['sentTo'] = sentTo,
print type(ticketJson['sentTo']), ticketJson['sentTo']

which outputs the following on my terminal:

<type 'str'> Pete Chasin
<type 'tuple'> ('Pete Chasin',)

Why does assigning it to a dict convert it to a tuple?

Answer 1

You told Python to create a tuple containing a string:

ticketJson['sentTo'] = sentTo,
#                            ^

It is the comma that defines a tuple. Parentheses are only needed to disambiguate a tuple from other uses of a comma, such as in a function call.

From the Parenthesized forms section :

Note that tuples are not formed by the parentheses, but rather by use of the comma operator. The exception is the empty tuple, for which parentheses are required — allowing unparenthesized “nothing” in expressions would cause ambiguities and allow common typos to pass uncaught.

and from Expression lists :

An expression list containing at least one comma yields a tuple. The length of the tuple is the number of expressions in the list. The expressions are evaluated from left to right.

Answer 2

ticketJson['sentTo'] = sentTo,是单元素元组