缘由：

在看一些Python代码的时候会发现有人在创建list/tuple的时候会在最后一个元素后面添加一个’逗号’，而且也不报错，对有一点强迫症的我来说这不可忍受，需要删掉。不过后来想想既然别人这么写应该还是有一定道理的，于是，就有了下文。

搜索关键字：

• python create a list with one more comma
• python create a tuple with one more comma

参考链接：

• http://stackoverflow.com/questions/11597901/why-does-python-allow-a-trailing-comma-in-list
• https://docs.python.org/2/tutorial/datastructures.html
• https://wiki.python.org/moin/TupleSyntax
• http://www.dotnetperls.com/tuple-python
• http://www.pythonlearn.com/html-009/book011.html

参考解答：

首先，在Python中创建一个list/tuple时，在最后一个元素后面添加一个’逗号’是没问题的；

其次，这样做的好处在于：在编辑“多行元素的list”时更不容易犯错(忘记添加/删除’逗号’)；以及在diff代码时更好的观感。

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The main advantages are that it makes multi-line lists easier to edit and that it reduces clutter in diffs.

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It’s a common syntactical convention to allow trailing commas in an array, languages like C and Java allow it, and Python seems to have adopted this convention for its list data structure. It’s particularly useful when generating code for populating a list: just generate a sequence of elements and commas, no need to consider the last one as an special case that doesn’t have a comma at the end.

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Python newbies often have some confusion about how to make one-element tuples. VenkataSubramanian provided a nice summary of Python’s tuple syntax [1].

Zero Element Tuples

In Python, zero-element tuples look like:

()

In this form, unlike the other tuple forms, parentheses are the essential elements, not commas.

One Element Tuples

One-element tuples look like:

1,

The essential element here is the trailing comma. As for any expression, parentheses are optional, so you may also write one-element tuples like

(1,)

but it is the comma, not the parentheses, that define the tuple.

Multiple Element Tuples

In Python, multiple-element tuples look like:

1,2,3

The essential elements are the commas between each element of the tuple. Multiple-element tuples may be written with a trailing comma, e.g.

1,2,3,

but the trailing comma is completely optional. Just like all other expressions in Python, multiple-element tuples may be enclosed in parentheses, e.g.

(1,2,3)

or

(1,2,3,)

but again, it is the commas, not the parentheses, that define the tuple.

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