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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def lock( ctx, state, **kwargs ):
 """Generates Pipfile.lock."""

    from ..core import ensure_project, do_init, do_lock

    # Ensure that virtualenv is available.
    ensure_project(three=state.three, python=state.python, pypi_mirror=state.pypi_mirror)
    if state.installstate.requirementstxt:
        do_init(
            dev=state.installstate.dev,
            requirements=state.installstate.requirementstxt,
            pypi_mirror=state.pypi_mirror,
            pre=state.installstate.pre,
        )
    do_lock(
        ctx=ctx,
        clear=state.clear,
        pre=state.installstate.pre,
        keep_outdated=state.installstate.keep_outdated,
        pypi_mirror=state.pypi_mirror,
    )