python列表理解不按预期工作

Question

我是python中列表理解的新手。我想将for-if语句转换为list comprehension，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)

我的清单理解：

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

comperhension已经返回一个列表，所以我认为list_new.append（成员）是多余的。

我在没有“记录”的情况下复制了您的代码，没有附加部分。它似乎有效：

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（在编辑问题后添加“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

Answer 2

试试这个：

method table not found in \illuminate\Support\Faces\DB

请注意，list_new = [member for member in a if record and "addRec" in member] 函数不会返回任何内容。