How do I split the definition of a long string over multiple lines?

Question:

I have a very long query. I would like to split it in several lines in Python. A way to do it in JavaScript would be using several sentences and joining them with a + operator (I know, maybe it’s not the most efficient way to do it, but I’m not really concerned about performance in this stage, just code readability). Example:

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

I tried doing something similar in Python, but it didn’t work, so I used to split the long string. However, I’m not sure if this is the only/best/pythonicest way of doing it. It looks awkward.
Actual code:

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
Asked By: Pablo Mescher

||

Answers:

Are you talking about multi-line strings? Easy, use triple quotes to start and end them.

s = """ this is a very
        long string if I had the
        energy to type more and more ..."""

You can use single quotes too (3 of them of course at start and end) and treat the resulting string s just like any other string.

NOTE: Just as with any string, anything between the starting and ending quotes becomes part of the string, so this example has a leading blank (as pointed out by @root45). This string will also contain both blanks and newlines.

I.e.,:

' this is a veryn        long string if I had then        energy to type more and more ...'

Finally, one can also construct long lines in Python like this:

 s = ("this is a very"
      "long string too"
      "for sure ..."
     )

which will not include any extra blanks or newlines (this is a deliberate example showing what the effect of skipping blanks will result in):

'this is a verylong string toofor sure ...'

No commas required, simply place the strings to be joined together into a pair of parenthesis and be sure to account for any needed blanks and newlines.

Answered By: Levon

Your actual code shouldn’t work; you are missing white spaces at the end of "lines" (for example, role.descr as roleFROM...).

There are triple quotes for multiline strings:

string = """line
  line2
  line3"""

It will contain the line breaks and extra spaces, but for SQL that’s not a problem.

Answered By: Karoly Horvath

If you don’t want a multiline string, but just have a long single line string, you can use parentheses. Just make sure you don’t include commas between the string segments (then it will be a tuple).

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)

In a SQL statement like what you’re constructing, multiline strings would also be fine. But if the extra white space a multiline string would contain would be a problem, then this would be a good way to achieve what you want.

As noted in the comments, concatenating SQL queries in this way is a SQL injection security risk waiting to happen, so use your database’s parameterized queries feature to prevent this. However, I’m leaving the answer as-is otherwise as it directly answers the question asked.

Answered By: Jesse

You can also place the SQL statement in a separate file, action.sql, and load it in the .py file with:

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

So the SQL statements will be separated from the Python code. If there are parameters in the SQL statement which needs to be filled from Python, you can use string formatting (like %s or {field}).

Answered By: mrijken

I found myself happy with this one:

string = """This is a
very long string,
containing commas,
that I split up
for readability""".replace('n',' ')
Answered By: Eero Aaltonen

I find that when building long strings, you are usually doing something like building an SQL query, in which case this is best:

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

What Levon suggested is good, but it might be vulnerable to mistakes:

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

query == "SELECT fooFROM barWHERE baz"  # Probably not what you want
Answered By: darkfeline

Breaking lines by works for me. Here is an example:

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

I use a recursive function to build complex SQL queries. This technique can generally be used to build large strings while maintaining code readability.

# Utility function to recursively resolve SQL statements.
# CAUTION: Use this function carefully, Pass correct SQL parameters {},
# TODO: This should never happen but check for infinite loops
def resolveSQL(sql_seed, sqlparams):
    sql = sql_seed % (sqlparams)
    if sql == sql_seed:
        return ' '.join([x.strip() for x in sql.split()])
    else:
        return resolveSQL(sql, sqlparams)

P.S.: Have a look at the awesome python-sqlparse library to pretty print SQL queries if needed.

Answered By: Sandeep

You can also include variables when using """ notation:

foo = '1234'

long_string = """fosdl a sdlfklaskdf as
as df ajsdfj asdfa sld
a sdf alsdfl alsdfl """ +  foo + """ aks
asdkfkasdk fak"""

A better way is, with named parameters and .format():

body = """
<html>
<head>
</head>
<body>
    <p>Lorem ipsum.</p>
    <dl>
        <dt>Asdf:</dt>     <dd><a href="{link}">{name}</a></dd>
    </dl>
    </body>
</html>
""".format(
    link='http://www.asdf.com',
    name='Asdf',
)

print(body)
Answered By: gjgjgj

For example:

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'

If the value of the condition should be a string, you can do it like this:

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'"
Answered By: pangpang

Another option that I think is more readable when the code (e.g., a variable) is indented and the output string should be a one-liner (no newlines):

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
Answered By: Eyal Levin

"À la" Scala way (but I think is the most Pythonic way as the OP demands):

description = """
            | The intention of this module is to provide a method to
            | pass meta information in markdown_ header files for
            | using it in jinja_ templates.
            |
            | Also, to provide a method to use markdown files as jinja
            | templates. Maybe you prefer to see the code than
            | to install it.""".replace('n            | n','n').replace('            | ',' ')

If you want final str without jump lines, just put n at the start of the first argument of the second replace:

.replace('n            | ',' ')`.

Note: the white line between "…templates." and "Also, …" requires a white space after the |.

Answered By: victe

In Python >= 3.6 you can use Formatted string literals (f string)

query= f'''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}'''
Answered By: Vlad Bezden

I like this approach because it privileges reading. In cases where we have long strings there is no way! Depending on the level of indentation you are in and still limited to 80 characters per line… Well… No need to say anything else

In my view, the Python style guides are still very vague. I took the Eero Aaltonen approach, because it privileges reading and common sense. I understand that style guides should help us and not make our lives a mess.

class ClassName():
    def method_name():
        if condition_0:
            if condition_1:
                if condition_2:
                    some_variable_0 =
"""
some_js_func_call(
    undefined,
    {
        'some_attr_0': 'value_0',
        'some_attr_1': 'value_1',
        'some_attr_2': '""" + some_variable_1 + """'
    },
    undefined,
    undefined,
    true
)
"""
Answered By: Eduardo Lucio

I personally find the following to be the best (simple, safe and Pythonic) way to write raw SQL queries in Python, especially when using Python’s sqlite3 module:

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

  • Neat and simple code (Pythonic!)
  • Safe from SQL injection
  • Compatible with both Python 2 and Python 3 (it’s Pythonic after all)
  • No string concatenation required
  • No need to ensure that the right-most character of each line is a space

Cons

  • Since variables in the query are replaced by the ? placeholder, it may become a little difficult to keep track of which ? is to be substituted by which Python variable when there are lots of them in the query.
Answered By: Faheel

This approach uses:

  • almost no internal punctuation by using a triple quoted string
  • strips away local indentation using the inspect module
  • uses Python 3.6 formatted string interpolation (‘f’) for the account_id and def_id variables.

This way looks the most Pythonic to me.

import inspect

query = inspect.cleandoc(f'''
    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}'''
)
Answered By: Christopher Bruns

I usually use something like this:

text = '''
    This string was typed to be a demo
    on how could we write a multi-line
    text in Python.
'''

If you want to remove annoying blank spaces in each line, you could do as follows:

text = 'n'.join(line.lstrip() for line in text.splitlines())
Answered By: Israel Barth Rubio

I find textwrap.dedent the best for long strings as described here:

def create_snippet():
    code_snippet = textwrap.dedent("""
        int main(int argc, char* argv[]) {
            return 0;
        }
    """)
    do_something(code_snippet)
Answered By: fredrik

Generally, I use list and join for multi-line comments/string.

lines = list()
lines.append('SELECT action.enter code here descr as "action", ')
lines.append('role.id as role_id,')
lines.append('role.descr as role')
lines.append('FROM ')
lines.append('public.role_action_def,')
lines.append('public.role,')
lines.append('public.record_def, ')
lines.append('public.action')
query = " ".join(lines)

You can use any string to join all these list elements, like ‘n‘(newline) or ‘,‘(comma) or ‘ ‘(space).

Answered By: paone

Others have mentioned the parentheses method already, but I’d like to add that with parentheses, inline comments are allowed.

Comment on each fragment:

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.
)

Comment not allowed after continuation:

When using backslash line continuations ( ), comments are not allowed. You’ll receive a SyntaxError: unexpected character after line continuation character error.

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

Better comments for Regex strings:

Based on the example from 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)
Answered By: ddrscott

Try something like this. Like in this format it will return you a continuous line like you have successfully enquired about this property:

"message": f'You have successfully inquired about '
           f'{enquiring_property.title} Property owned by '
           f'{enquiring_property.client}'
Answered By: Kelvin Onkundi

tl;dr: Use """ and """ to wrap the string, as in

string = """
This is a long string
spanning multiple lines.
"""

From the official Python documentation:

String literals can span multiple lines. One way is using
triple-quotes: """…""" or ”’…”’. End of lines are automatically
included in the string, but it’s possible to prevent this by adding a
at the end of the line. The following example:

print("""
Usage: thingy [OPTIONS]
     -h                        Display this usage message
     -H hostname               Hostname to connect to
""")

produces the following output (note that the initial newline is not
included):

Usage: thingy [OPTIONS]
     -h                        Display this usage message
     -H hostname               Hostname to connect to
Answered By: Flow

From the official Python documentation:

String literals can span multiple lines. One way is using
triple-quotes: """…""" or ”’…”’. End of lines are automatically
included in the string, but it’s possible to prevent this by adding a
at the end of the line. The following example:

print("""
Usage: thingy [OPTIONS]
     -h                        Display this usage message
     -H hostname               Hostname to connect to
""")

produces the following output (note that the initial newline is not
included):

Answered By: Flow

For defining a long string inside a dict,
keeping the newlines but omitting the spaces, I ended up defining the string in a constant like this:

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

my_dict = {
   'foo': 'bar',
   'string': LONG_STRING
}
Answered By: flix

As a general approach to long strings in Python, you can use triple quotes, split and join:

_str = ' '.join('''Lorem ipsum dolor sit amet, consectetur adipiscing
        elit, sed do eiusmod tempor incididunt ut labore et dolore
        magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation
        ullamco laboris nisi ut aliquip ex ea commodo.'''.split())

Output:

'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo.'

With regard to OP’s question relating to a SQL query, the answer below disregards the correctness of this approach to building SQL queries and focuses only on building long strings in a readable and aesthetic way without additional imports. It also disregards the computational load this entails.

Using triple quotes, we build a long and readable string which we then break up into a list using split() thereby stripping the white space and then join it back together with ' '.join(). Finally we insert the variables using the format() command:

account_id = 123
def_id = 321

_str = '''
    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 = {}
    '''

query = ' '.join(_str.split()).format(account_id, account_id, def_id)

Produces:

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 = 123 AND record_def.account_id=123 AND def_id=321

This approach is not in line with PEP 8, but I find it useful at times.

Please note that the curly brackets in the original string are used by the format() function.

Answered By: Rasmus Groth

Combining the ideas from:

Levon or Jesse, Faheel and ddrscott

with my formatting suggestion, you could write your query as:

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
         )

 vars = (account_id, account_id, def_id)     # A tuple of the query variables
 cursor.execute(query, vars)                 # Using Python's sqlite3 module

Or like:

vars = []
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 = '
                 vars.append(account_id) or '?'
             ' AND'
             ' record_def.account_id = '
                 vars.append(account_id) or '?'
             ' AND'
             ' def_id = '
                 vars.append(def_id) or '?'
         )

 cursor.execute(query, tuple(vars))  # Using Python's sqlite3 module

Which could be interesting together with ‘IN’ and ‘vars.extend(options) or n_options(len(options))’, where:

def n_options(count):
    return '(' + ','.join(count*'?') + ')'

Or with the hint from darkfeline, that you might still make mistakes with those leading spaces and separators and also with named placeholders:

SPACE_SEP = ' '
COMMA_SEP = ', '
AND_SEP   = ' AND '

query = SPACE_SEP.join((
    'SELECT',
        COMMA_SEP.join((
        'action.descr as "action"',
        'role.id as role_id',
        'role.descr as role',
        )),
    'FROM',
        COMMA_SEP.join((
        'public.role_action_def',
        'public.role',
        'public.record_def',
        'public.action',
        )),
    'WHERE',
        AND_SEP.join((
        'role.id = role_action_def.role_id',
        'record_def.id = role_action_def.def_id',
        'action.id = role_action_def.action_id',
        'role_action_def.account_id = :account_id',
        'record_def.account_id = :account_id',
        'def_id = :def_id',
        )),
    ))

vars = {'account_id':account_id,'def_id':def_id}  # A dictionary of the query variables
cursor.execute(query, vars)                       # Using Python's sqlite3 module

See documentation of Cursor.execute-function.

"This is the [most Pythonic] way!" – …

Answered By: e.d.n.a

Adding to @Levon’s answer….

1. Create a multiline string like this:

paragraph = """this is a very
        long string if I had the
        energy to type more and more ..."""

print(paragraph)

Output:

'this is a veryn        long string if I had then        energy to type more and more ...'

This string will have newlines and blank spaces. So remove them.

2. Remove extra spaces using regex

paragraph = re.sub('s+', ' ', paragraph)
print(paragraph)

Ouput:

'this is a very long string if I had the energy to type more and more ...'
Answered By: user41855

I know it’s a rather old question, but Python has changed in the meantime and I don’t see this answer, so here we go.

Another way is to use to cut the current line and move to another:

print("This line will 
get carried over to
 the new line.
Notice how this
word will be together because 
of no space around it")

Ummm.

I know it’s been a long time since this question got posted.
But I just found the style I would like to use to assign long and multiline strings to variables in my projects.
This takes a bit of extra runtime, but still preserves the beauty of the code, even if the variable I am assigning my string to is heavily indented.

    # Suppose the following code is heavily indented
    line3header = "Third"

    variable = fr"""

First line.
Second line.
{line3header} line.
{{}} line.
...
The last line.

    """.strip()
    """A variable whose name is Variable.

    You can even add a docstring here.
    """

    variable = variable.format("Fourth")
    print(variable)
    variable += "n"
    print(variable, end="")

There it goes.

Answered By: Rick