How to use the jupytext.writes function in jupytext

def test_identity_source_write_read(nb_file):
    """Test that writing the notebook with jupytext, and read again,
    is the same as removing outputs"""

    with open(nb_file) as fp:
        nb1 = nbformat.read(fp, as_version=4)

    py = jupytext.writes(nb1, 'py')
    nb2 = jupytext.reads(py, 'py')

    compare_notebooks(nb2, nb1)

def test_identity_source_write_read(nb_file, ext):
    """
    Test that writing the notebook with R, and read again,
    is the same as removing outputs
    """

    with open(nb_file) as fp:
        nb1 = nbformat.read(fp, as_version=4)

    R = jupytext.writes(nb1, ext)
    nb2 = jupytext.reads(R, ext)

    compare_notebooks(nb2, nb1)

def test_active_ipynb_rspin(no_jupytext_version_number):
    nb = jupytext.reads(ACTIVE_IPYNB_RSPIN['.R'], 'R:spin')
    assert len(nb.cells) == 1
    compare(jupytext.writes(nb, 'R:spin'), ACTIVE_IPYNB_RSPIN['.R'])
    compare(nb.cells[0], ACTIVE_IPYNB_RSPIN['.ipynb'])

# Examples
```jldoctest
julia> cube(2)
8

""" function cube(x) x^3 end''' assert nb.cells[1].cell_type == 'code' assert nb.cells[1].source == 'cube(x)' assert nb.cells[2].cell_type == 'markdown' compare(nb.cells[2].source, 'And a markdown comment')

julia2 = jupytext.writes(nb, 'jl')
compare(julia2, julia)

def test_ipynb_to_percent_to_light(nb_file):
    nb = jupytext.read(nb_file)
    pct = jupytext.writes(nb, 'auto:percent')
    auto_ext = auto_ext_from_metadata(nb.metadata)
    comment = _SCRIPT_EXTENSIONS[auto_ext]['comment']
    lgt = (pct.replace(comment + ' %%\n', comment + ' +\n')
           .replace(comment + ' %% ', comment + ' + ')
           .replace(comment + '       format_name: percent', comment + '       format_name: light'))
    nb2 = jupytext.reads(lgt, auto_ext)
    compare_notebooks(nb2, nb)

display_name: Python 3
    language: python
    name: python3
---

```python2
a = 1
print a

b = 2
print(b)

"""): md = jupytext.writes(nb, 'md') compare(md, text)

nb2 = jupytext.reads(md, 'md')
compare_notebooks(nb2, nb)

# it's better not to have Jupytext metadata in test notebooks:
    if fmt == 'ipynb' and 'jupytext' in notebook.metadata:  # pragma: no cover
        notebook.metadata.pop('jupytext')
        jupytext.write(nb_file, fmt=fmt)

    create_mirror_file_if_missing(mirror_file, notebook, fmt)

    # Compare the text representation of the two notebooks
    if compare_notebook:
        nb_mirror = jupytext.read(mirror_file)
        compare(nb_mirror, notebook)
        return
    elif ext == '.ipynb':
        notebook = jupytext.read(mirror_file)
        fmt.update({'extension': org_ext})
        actual = jupytext.writes(notebook, fmt)
        with open(nb_file, encoding='utf-8') as fp:
            expected = fp.read()
    else:
        actual = jupytext.writes(notebook, fmt)
        with open(mirror_file, encoding='utf-8') as fp:
            expected = fp.read()

    if not actual.endswith('\n'):
        actual = actual + '\n'
    compare(actual, expected)

    # Compare the two notebooks
    if ext != '.ipynb':
        notebook = jupytext.read(nb_file)
        nb_mirror = jupytext.read(mirror_file, fmt=fmt)

key: value
---
""", target="""---
jupyter:
  extra:
    key: value
  jupytext:
    notebook_metadata_filter: extra
  kernelspec:
    display_name: Python 3
    language: python
    name: python3
---
"""):
    nb = jupytext.reads(org, 'md')
    text = jupytext.writes(nb, 'md')
    compare(text, target)

pass


# %% a function
def f(x):
    return 42 * x

"""):
    nb = jupytext.reads(script, 'py')
    assert len(nb.cells) == 5
    for i in range(5):
        assert nb.cells[i].cell_type == 'code'
        assert not nb.cells[i].source.startswith('\n')
        assert not nb.cells[i].source.endswith('\n')

    script2 = jupytext.writes(nb, 'py:hydrogen')
    compare(script2, script)

def test_read_julia_notebook(markdown="""```julia
1 + 1

"""): nb = jupytext.reads(markdown, 'md') assert nb.metadata['jupytext']['main_language'] == 'julia' assert len(nb.cells) == 1 assert nb.cells[0].cell_type == 'code' markdown2 = jupytext.writes(nb, 'md') compare(markdown2, markdown)