Python 條件迭代的列表理解

Question

只是想問一下這組特定的代碼是否可以表示為單行列表理解：

files = ["country_Maldives", "country_East Timor", "country_Laos", "country_Uruguay"]
accountlist = ["Laos", "Maldives"]

final_list = []
for account in accountlist:
    included = [file for file in files if account in file][0]
    final_list.append(included)

謝謝你。

Answer 1

由於您的代碼只是獲取所有匹配項並選擇第一個匹配項：

[file for file in files if account in file][0]

您可以改為使用next()繼續檢索下一項，直到找到匹配項：

result = [next(file for file in files if account in file) for account in accountlist]

print(result)
# ['country_Laos', 'country_Maldives'] => Same output as your original code

上面的唯一問題是，如果迭代器用盡並且找不到匹配項，則會引發StopIteration異常。 為了防止這種情況，我們可以提供一個默認值，例如None ，所以它返回這個值而不是異常。

[next((file for file in files if account in file), None) for account in accountlist]

然后，如果我們想過濾掉None匹配項，我們可以使用另一個列表推導來做到這一點：

filtered = [file for file in result if file is not None]

Answer 2

查看any/all運算符：

ret = [file for file in files if any(account in file for account in accountlist)]

https://docs.python.org/3/library/functions.html#any

UDP

上面的 Oneliner 返回所有文件的列表，每個文件都包含任何帳戶。 如果您只想按給定條件查找第一個條目，運算符next也值得一提：

ret = [next((file for file in files if account in file), []) for account in accountlist]

https://docs.python.org/3/library/functions.html#next

Answer 3

只是另一種方式，嵌套for循環......

In [19]: files = ["country_Maldives", "country_East Timor", "country_Laos", "country_Uruguay"]
    ...: accountlist = ["Laos", "Maldives"]

In [20]: res=[file  for acc in accountlist for file in files  if acc in file.split('_')]

In [21]: res
Out[21]: ['country_Laos', 'country_Maldives']