black adds unnecessary lines around triple-quoted blocks

[webartifex]

Using the rpy2 library to embed R code in a Python project, a common idiom is this:

import rpy2.robjects as robjects

robjects.r('''
loadRData <- function(fileName){
    #' Load an .rda file and return it as a r.DataFrame.
    load(fileName)
    get(ls()[ls() != "fileName"])
}
''')

Appying black -S to it, the code becomes:

robjects.r(
    '''
loadRData <- function(fileName){
    #' Load an .rda file and return it as a r.DataFrame.
    load(fileName)
    get(ls()[ls() != "fileName"])
}
'''
)

This might be an issue with other language embeddings as well.

My suggestion is that black does not change this idiom, i.e., the opening and closing parenthesis should be coalesced with the triple (single) quotes.

Operating system:
Python version: 3.6.5
Black version: 18.6b4
Does also happen on master: yes

EDIT: earlier versions did not show the whitespace correctly.

[asottile]

To make a code block use triple backticks

    ```python
    print('like this!')
    ```

[gwax]

I have run into this with the similar textwrap.dedent idiom:

textwrap.dedent("""\
    Hello, I am
    a multiline string used with
    a common idiom
""")

black will convert this to:

textwrap.dedent(
    """\
    Hello, I am
    a multiline string used with
    a common idiom
"""
)

This is particularly bad in the case of another containing function:

sqlalchemy.text(textwrap.dedent("""\
    SELECT
        *
    FROM
        sometable
"""))

becomes:

sqlalchemy.text(
    textwrap.dedent(
        """\
    SELECT
        *
    FROM
        sometable
"""
    )
)

[zsol]

I think this boils down to the same cause as #256

[ambv]

I'll close this as a duplicate and we'll handle this use case as part of #256, too.