我有一个很长的疑问。我想用Python将它分成几行。在JavaScript中实现这一点的一种方法是使用几个句子并用+运算符将它们连接起来(我知道,也许这不是最有效的方法,但我并不真正关心这个阶段的性能,只是代码的可读性)。例子:

var long_string = 'some text not important. just garbage to' +
                      'illustrate my example';

我尝试在Python中做类似的事情,但没有成功,所以我使用了\来拆分长字符串。然而,我不确定这是否是唯一/最好/最蟒蛇的做法。看起来很尴尬。实际代码:

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

当前回答

我认为当代码(例如,变量)缩进并且输出字符串应该是单行(没有换行)时,另一个选项更可读:

def some_method():

    long_string = """
A presumptuous long string
which looks a bit nicer
in a text editor when
written over multiple lines
""".strip('\n').replace('\n', ' ')

    return long_string

其他回答

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})。

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

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。

用\换行对我很有用。下面是一个例子:

longStr = "This is a very long string " \
        "that I wrote to help somebody " \
        "who had a question about " \
        "writing long strings in Python"

例如:

sql = ("select field1, field2, field3, field4 "
       "from table "
       "where condition1={} "
       "and condition2={}").format(1, 2)

Output: 'select field1, field2, field3, field4 from table
         where condition1=1 and condition2=2'

如果条件的值应该是字符串,可以这样做:

sql = ("select field1, field2, field3, field4 "
       "from table "
       "where condition1='{0}' "
       "and condition2='{1}'").format('2016-10-12', '2017-10-12')

Output: "select field1, field2, field3, field4 from table where
         condition1='2016-10-12' and condition2='2017-10-12'"