您还可以将SQL语句放置在单独的文件action.SQL中，并使用以下命令将其加载到.py文件中：

with open('action.sql') as f:
   query = f.read()

因此，SQL语句将与Python代码分离。如果SQL语句中有需要从Python填充的参数，则可以使用字符串格式（如%s或｛field｝）。

为了在字典内定义长字符串，保留换行符但省略空格，我最终以如下常量定义字符串：

LONG_STRING = \
"""
This is a long sting
that contains newlines.
The newlines are important.
"""

my_dict = {
   'foo': 'bar',
   'string': LONG_STRING
}

如果不需要多行字符串，而只需要一个长的单行字符串，则可以使用括号。只需确保字符串段之间不包含逗号（那么它将是一个元组）。

query = ('SELECT   action.descr as "action", '
         'role.id as role_id,'
         'role.descr as role'
         ' FROM '
         'public.role_action_def,'
         'public.role,'
         'public.record_def, '
         'public.action'
         ' WHERE role.id = role_action_def.role_id AND'
         ' record_def.id = role_action_def.def_id AND'
         ' action.id = role_action_def.action_id AND'
         ' role_action_def.account_id = '+account_id+' AND'
         ' record_def.account_id='+account_id+' AND'
         ' def_id='+def_id)

在您正在构建的SQL语句中，多行字符串也可以。但是，如果多行字符串包含的额外空白是一个问题，那么这将是一个实现您所需功能的好方法。

如注释中所述，以这种方式连接SQL查询是SQL注入安全风险，因此请使用数据库的参数化查询功能来防止这种情况发生。然而，我保留了答案，因为它直接回答了问题。

我发现，当构建长字符串时，您通常会做一些类似于构建SQL查询的事情，在这种情况下，这是最好的：

query = ' '.join((  # Note double parentheses. join() takes an iterable
    "SELECT foo",
    "FROM bar",
    "WHERE baz",
))

Levon的建议很好，但可能容易出错：

query = (
    "SELECT foo"
    "FROM bar"
    "WHERE baz"
)

query == "SELECT fooFROM barWHERE baz"  # Probably not what you want

其他人已经提到了圆括号方法，但我想补充一点，使用圆括号时，允许内联注释。

对每个片段的注释：

nursery_rhyme = (
    'Mary had a little lamb,'          # Comments are great!
    'its fleece was white as snow.'
    'And everywhere that Mary went,'
    'her sheep would surely go.'       # What a pesky sheep.
)

继续后不允许注释：

使用反斜杠行延续符（\）时，不允许使用注释。您将收到一个SyntaxError：一行接一行的连续字符错误。

nursery_rhyme = 'Mary had a little lamb,' \  # These comments
    'its fleece was white as snow.'       \  # are invalid!
    'And everywhere that Mary went,'      \
    'her sheep would surely go.'
# => SyntaxError: unexpected character after line continuation character

Regex字符串的更好注释：

基于以下示例https://docs.python.org/3/library/re.html#re.VERBOSE,

a = re.compile(
    r'\d+'  # the integral part
    r'\.'   # the decimal point
    r'\d*'  # some fractional digits
)

# Using VERBOSE flag, IDE usually can't syntax highight the string comment.
a = re.compile(r"""\d +  # the integral part
                   \.    # the decimal point
                   \d *  # some fractional digits""", re.X)

我个人认为，以下是用Python编写原始SQL查询的最佳（简单、安全和Python化）方法，尤其是在使用Python的sqlite3模块时：

query = '''
    SELECT
        action.descr as action,
        role.id as role_id,
        role.descr as role
    FROM
        public.role_action_def,
        public.role,
        public.record_def,
        public.action
    WHERE
        role.id = role_action_def.role_id
        AND record_def.id = role_action_def.def_id
        AND action.id = role_action_def.action_id
        AND role_action_def.account_id = ?
        AND record_def.account_id = ?
        AND def_id = ?
'''
vars = (account_id, account_id, def_id)   # a tuple of query variables
cursor.execute(query, vars)   # using Python's sqlite3 module

Pros

整洁而简单的代码（Pythonic！）避免SQL注入与Python 2和Python 3兼容（毕竟是Pythonic）不需要字符串串联无需确保每行最右边的字符是空格

Cons

由于查询中的变量被替换为？占位符，它可能会变得有点难以跟踪哪个？当查询中有很多Python变量时，将由哪个Python变量替换。