Python：如果元素不在列表中，则添加到新列表

Question

我有一个看起来很丑陋的函数，并认为必须有一种更Python化的方式来执行此操作（大写字母变量是字符串）：

def get_missing_header_fields(header):
    missing_fields = []
    if FIRST_NAME not in header:
        missing_fields.append(FIRST_NAME)
    if LAST_NAME not in header:
        missing_fields.append(LAST_NAME)
    if EMAIL not in header:
        missing_fields.append(EMAIL)
    if PHONE not in header:
        missing_fields.append(PHONE)
    if ADDRESS not in header:
        missing_fields.append(ADDRESS)
    if COMPANY not in header:
        missing_fields.append(COMPANY)
    if TITLE not in header:
        missing_fields.append(TITLE)
    return missing_fields

有记录吗？

Answer 1

您可以为此使用集合：

FIELDS = set([FIRST_NAME, LAST_NAME, EMAIL, etc...])

def get_missing_header_fields(header):
  return FIELDS.difference(header)

集合是iterables并支持成员资格测试，通常对于大多数用例而言就足够了。 如果您真的需要一个列表，只需构造一个： list(FIELDS.difference(header))

Answer 2

只是理解

def get_missing_header_fields(header):
    # Completing the tuple is an exercise for the reader
    fields = (FIRST_NAME, LAST_NAME, ..., TITLE)
    return [field for field in fields if field not in header]

甚至一套

def get_missing_header_fields(header):
    # Completing the tuple is an exercise for the reader
    fields = set(FIRST_NAME, LAST_NAME, ..., TITLE)
    return list(fields - set(header))