在Python列表中插入值

Question

我正在研究解析文本文件的腳本，嘗試將其標準化爲足以將其插入到數據庫中。數據表示由1位或更多作者撰寫的文章。我遇到的問題是因爲沒有固定數量的作者，所以我在輸出文本文件中獲得可變數量的列。例如。

author1, author2, author3, this is the title of the article 
author1, author2, this is the title of the article 
author1, author2, author3, author4, this is the title of the article 

這些結果給我5.最大列數因此，對於第2篇文章中，我將需要添加空白列，以便輸出具有偶數列。什麼是最好的方法來做到這一點？我的輸入文本是製表符分隔的，我可以通過在選項卡上分割來很容易地遍歷它們。

Answer 1

假設你已經有了最大數量的列，並且已經將它們分成了列表（我假設你把它們放到了自己的列表中），你應該可以使用list.insert（ - 1，項目）來添加空列：

def columnize(mylists, maxcolumns): 
    for i in mylists: 
     while len(i) < maxcolumns: 
      i.insert(-1,None) 

mylists = [["author1","author2","author3","this is the title of the article"], 
      ["author1","author2","this is the title of the article"], 
      ["author1","author2","author3","author4","this is the title of the article"]] 

columnize(mylists,5) 
print mylists 

[['author1', 'author2', 'author3', None, 'this is the title of the article'], ['author1', 'author2', None, None, 'this is the title of the article'], ['author1', 'author2', 'author3', 'author4', 'this is the title of the article']] 

不破壞原來的列表，列表解析法替代版本：

def columnize(mylists, maxcolumns): 
    return [j[:-1]+([None]*(maxcolumns-len(j)))+j[-1:] for j in mylists] 

print columnize(mylists,5) 

[['author1', 'author2', 'author3', None, 'this is the title of the article'], ['author1', 'author2', None, None, 'this is the title of the article'], ['author1', 'author2', 'author3', 'author4', 'this is the title of the article']] 

Answer 2

原諒我，如果我誤解了，但它聽起來像你正在以一種困難的方式接近這個問題。這是很容易的文本文件轉換成映射標題一套作者的字典：

>>> lines = ["auth1, auth2, auth3, article1", "auth1, auth2, article2","auth1, article3"] 
>>> d = dict((x[-1], x[:-1]) for x in [line.split(', ') for line in lines]) 
>>> d 
{'article2': ['auth1', 'auth2'], 'article3': ['auth1'], 'article1': ['auth1', 'auth2', 'auth3']} 
>>> total_articles = len(d) 
>>> total_articles 
3 
>>> max_authors = max(len(val) for val in d.values()) 
>>> max_authors 
3 
>>> for k,v in d.iteritems(): 
...  print k 
...  print v + [None]*(max_authors-len(v)) 
... 
article2 
['auth1', 'auth2', None] 
article3 
['auth1', None, None] 
article1 
['auth1', 'auth2', 'auth3'] 

然後，如果你真的想，你可以輸出這個數據使用的內置到Python的csv module。或者，您可以直接輸出您將需要的SQL。

您正在多次打開同一個文件並多次讀取它，以獲取可從內存中的數據導出的計數。爲了這些目的，請勿多次讀取文件。