人生苦短
早用Python
這是工作中遇到的一個坑，首先看一下問題
raw_list = [["百度", "CPY"], ["京東", "CPY"], ["黃軒", "PN"], ["百度", "CPY"]]
列表嵌套了列表，并且有一個重復(fù)列表["百度", "CPY"]，現(xiàn)在要求將這個重復(fù)元素進(jìn)行去重（重復(fù)是指嵌套的列表內(nèi)兩個元素都相同），并且保證元素順序不變，輸出還是嵌套列表，即最后結(jié)果應(yīng)該長這樣：[["百度", "CPY"], ["京東", "CPY"], ["黃軒", "PN"]]
正常Python去重都是使用set，所以我這邊也是用這種思想處理一下
In [8]: new_list = [list(t) for t in set(tuple(_) for _ in raw_list)]
In [9]: new_list
Out[9]: [['京東', 'CPY'], ['百度', 'CPY'], ['黃軒', 'PN']]
=。=以為大功告成，結(jié)果發(fā)現(xiàn)嵌套列表順序變了
好吧一步步找一下是從哪邊順序變了的
In [10]: s = set(tuple(_) for _ in raw_list)
In [11]: s
Out[11]: {('京東', 'CPY'), ('百度', 'CPY'), ('黃軒', 'PN')}
恍然大悟關(guān)于set的兩個關(guān)鍵詞：無序 和 不重復(fù) =。=
所以從set解決排序問題基本無望了，然而我還沒有放棄，現(xiàn)在問題就變成了對于new_list怎么按照raw_list元素順序排序，當(dāng)然肯定要通過sort實現(xiàn)
翻一下Python文檔找到以下一段話
文檔地址
sort(*, key=None, reverse=False)
This method sorts the list in place, using only < comparisons between
items. Exceptions are not suppressed - if any comparison operations
fail, the entire sort operation will fail (and the list will likely be left in a
partially modified state).
[`sort()`](https://docs.python.org/3/library/stdtypes.html?highlight=sort#list.sort "list.sort")
accepts two arguments that can only be passed by keyword ( [keyword-only arguments](https://docs.python.org/3/glossary.html#keyword-only-parameter) ):
key specifies a function of one argument that is used to extract a
comparison key from each list element (for example, key=str.lower).
The key corresponding to each item in the list is calculated once and then used for the entire sorting process. The default value of None
means that list items are sorted directly without calculating a separate
key value.
開始劃重點：
sort方法通過參數(shù)key指定一個方法，換句話說，key參數(shù)的值是函數(shù)。
這個函數(shù)和new_list上的每個元素會產(chǎn)生一個結(jié)果，sort通過這個結(jié)果進(jìn)行排序。
于是這里就想到求出new_list里的每一個元素在raw_list里的索引，根據(jù)這個索引進(jìn)行排序。
代碼實現(xiàn)如下：
In [13]: new_list.sort(key=raw_list.index)
In [14]: new_list
Out[14]: [['百度', 'CPY'], ['京東', 'CPY'], ['黃軒', 'PN']]
結(jié)果和期望一樣 =。=
