python列表理解没有按预期工作

Question

我是 python 列表理解的新手。我想将 for-if 语句转换为列表理解，但它没有按预期工作：

a = ['Done', 'add dns addRec test 11.11.11.11']
record = "addRec"

普通python代码：

list_new = []    
for member in a:
  if record and "addRec" in member:
    list_new.append(member)
    print(list_new)

我的列表理解：

list_new = [list_new.append(member) for member in a if record and "addRec" in member]

list_new 作为空列表返回。

它应该返回：

['add dns addRec test 11.11.11.11']

Answer 1

试试这个：

list_new = [member for member in a if record and "addRec" in member]

请注意，.append() 函数不会返回任何内容。

Answer 2

comperhension 已经返回了一个列表，所以我认为 list_new.append(member) 是多余的。

我在没有“记录”和附加部分的情况下复制了您的代码。它似乎正在工作：

a = ['Done', 'add dns addRec test 11.11.11.11']
list_new = []
for member in a:
  if "addRec" in member:
    list_new.append(member)
    print(list_new)
assert ['add dns addRec test 11.11.11.11'] == list_new

#comperhension
list_new = [member for member in a if "addRec" in member]
print list_new
assert ['add dns addRec test 11.11.11.11'] == list_new

编辑（在问题编辑后添加“记录”）：

a = ['Done', 'add dns addRec test 11.11.11.11']
record = "addRec"

list_new = []
for member in a:
  if record and "addRec" in member:
    list_new.append(member)
    print(list_new)
assert ['add dns addRec test 11.11.11.11'] == list_new

#comperhension
list_new = [member for member in a if record and "addRec" in member]
print list_new
assert ['add dns addRec test 11.11.11.11'] == list_new