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
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
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。
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)
你说的是多行字符串吗?简单,使用三引号开始和结束它们。
s = """ this is a very
long string if I had the
energy to type more and more ..."""
您也可以使用单引号(当然,在开始和结束处有3个引号),并像对待任何其他字符串一样对待生成的字符串。
注意:与任何字符串一样,起始引号和结束引号之间的任何内容都将成为字符串的一部分,因此本示例有一个前导空格(如@root45所指出的)。此字符串还将包含空格和换行符。
即。,:
' this is a very\n long string if I had the\n energy to type more and more ...'
最后,您还可以在Python中构造如下的长行:
s = ("this is a very"
"long string too"
"for sure ..."
)
这将不包括任何额外的空格或换行符(这是一个故意的示例,显示跳过空格的效果):
'this is a verylong string toofor sure ...'
不需要逗号,只需将要连接在一起的字符串放入一对括号中,并确保考虑到任何需要的空格和换行符。
tl;dr:使用“”和“”来换行字符串,如中所示
string = """\
This is a long string
spanning multiple lines.
"""
从Python官方文档中:
字符串文本可以跨越多行。一种方法是使用三引号:“”“…”“”或“”“”…“”。行的结束是自动的包含在字符串中,但可以通过添加\在线路的末端。以下示例:
print("""\
Usage: thingy [OPTIONS]
-h Display this usage message
-H hostname Hostname to connect to
""")
生成以下输出(注意,初始换行符不是包括在内):
Usage: thingy [OPTIONS]
-h Display this usage message
-H hostname Hostname to connect to