Fixed some pep8 violations and updated grid docs (#55)

Author: babbush

src/fermilib/utils/_grid.py

@@ -25,7 +25,7 @@ def __init__(self, dimensions, length, scale):
         Args:
             dimensions (int): The number of dimensions the grid lives in.
             length (int): The number of points along each grid axis.
-            scale (float): The distance between adjacent grid points.
+            scale (float): The total length of each grid dimension.
         """
         if not isinstance(dimensions, int) or dimensions < 0:
             raise ValueError(
@@ -49,14 +49,14 @@ def volume_scale(self):
         Returns:
             float: The volume of a length-scale hypercube within the grid.
         """
-        return self.scale**float(self.dimensions)
+        return self.scale ** float(self.dimensions)
 
     def num_points(self):
         """
         Returns:
             int: The number of points in the grid.
         """
-        return self.length**self.dimensions
+        return self.length ** self.dimensions
 
     def all_points_indices(self):
         """

src/fermilib/utils/_jellium_test.py

@@ -136,9 +136,8 @@ def test_kinetic_integration(self):
 
     def test_potential_integration(self):
 
-        # Compute potential energy operator in both momentum and position
-        # space.
-        grid = Grid(dimensions=2, length=3, scale = 2.)
+        # Compute potential energy operator in momentum and position space.
+        grid = Grid(dimensions=2, length=3, scale=2.)
         spinless = 1
         momentum_potential = momentum_potential_operator(grid, spinless)
         position_potential = position_potential_operator(grid, spinless)

src/fermilib/utils/_plane_wave_hamiltonian.py

@@ -54,7 +54,8 @@ def dual_basis_u_operator(grid, geometry, spinless):
                     continue
                 exp_index = 1.0j * momenta.dot(coordinate_j - coordinate_p)
                 coefficient = (prefactor / momenta_squared *
-                    periodic_hash_table[nuclear_term[0]] * numpy.exp(exp_index))
+                               periodic_hash_table[nuclear_term[0]] *
+                               numpy.exp(exp_index))
 
                 for spin_p in spins:
                     orbital_p = orbital_id(
@@ -103,7 +104,8 @@ def plane_wave_u_operator(grid, geometry, spinless):
                 coordinate_j = numpy.array(nuclear_term[1])
                 exp_index = 1.0j * momenta_p_q.dot(coordinate_j)
                 coefficient = (prefactor / momenta_p_q_squared *
-                    periodic_hash_table[nuclear_term[0]] * numpy.exp(exp_index))
+                               periodic_hash_table[nuclear_term[0]] *
+                               numpy.exp(exp_index))
 
                 for spin in spins:
                     orbital_p = orbital_id(grid.length, indices_p, spin)