code: def cf_to_proj(var):
      r
      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)
docs: 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.