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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 cf_to_proj(var):
 r"""Convert a Variable with projection information to a Proj.4 Projection instance. The attributes of this Variable must conform to the Climate and Forecasting (CF) netCDF conventions. Parameters var : Variable The projection variable with appropriate attributes. """

    import pyproj
    kwargs = {'lat_0': var.latitude_of_projection_origin, 'a': var.earth_radius,
              'b': var.earth_radius}
    if var.grid_mapping_name == 'lambert_conformal_conic':
        kwargs['proj'] = 'lcc'
        kwargs['lon_0'] = var.longitude_of_central_meridian
        kwargs['lat_1'] = var.standard_parallel
        kwargs['lat_2'] = var.standard_parallel
    elif var.grid_mapping_name == 'polar_stereographic':
        kwargs['proj'] = 'stere'
        kwargs['lon_0'] = var.straight_vertical_longitude_from_pole
        kwargs['lat_0'] = var.latitude_of_projection_origin
        kwargs['lat_ts'] = var.standard_parallel
        kwargs['x_0'] = False  # Easting
        kwargs['y_0'] = False  # Northing
    elif var.grid_mapping_name == 'mercator':
        kwargs['proj'] = 'merc'
        kwargs['lon_0'] = var.longitude_of_projection_origin
        kwargs['lat_ts'] = var.standard_parallel
        kwargs['x_0'] = False  # Easting
        kwargs['y_0'] = False  # Northing

    return pyproj.Proj(**kwargs)