Python NumPy (Page: 6)

import numpy as np

def unit_vector(vector):
    """ Calculate Unit Vector  """
    return vector / np.linalg.norm(vector)

def angle_between(v1, v2, radian = True):
    """ Angle between vectors is arrcos from scalar (dot) product
        of tweo unit vectors """
    v1_u = unit_vector(v1)
    v2_u = unit_vector(v2)
    ang = np.arccos(np.clip(np.dot(v1_u, v2_u), -1.0, 1.0))
    if radian: return ang
    return np.rad2deg(ang)

v1 = (1, 0, 0)
v2 = (0, 1, 0)

print(angle_between(v1, v2, False)) # 90.0

import numpy as np

def rotate_2d(vector, theta, radian = True):
    """Rotate vector by given angle"""
    if not radian: theta = np.deg2rad(theta)
    c, s = np.cos(theta), np.sin(theta)
    rot = np.array([[c, -s],
                    [s,  c]
                  ])
    return np.dot(rot, vector)

print(rotate_2d([1, 0], -45, False)) # [ 0.70710678 -0.70710678]

def rotation_matrix_from_vectors(v1, v2):
    """ Find the rotation matrix that aligns 3D v1 to v2
    :return mat: A transform matrix (3x3) which when applied to v1, aligns it with v2.
    """
    a = v1 / np.linalg.norm(v1)
    b = v2 / np.linalg.norm(v2)
    v = np.cross(a, b)
    if not any(v): return np.eye(3) #vectors are parallel
    c = np.dot(a, b)
    s = np.linalg.norm(v)
    kmat = np.array([[0, -v[2], v[1]], [v[2], 0, -v[0]], [-v[1], v[0], 0]])
    rotation_matrix = np.eye(3) + kmat + kmat.dot(kmat) * ((1 - c) / (s ** 2))
    return rotation_matrix

# TESTS
vec1 = [1, 0, 0]
vec2 = [0, 2, 0]

mat = rotation_matrix_from_vectors(vec1, vec2)
vec1_rot = mat.dot(vec1)
print( mat )    # [[ 0. -1.  0.]  [ 1.  0.  0.]  [ 0.  0.  1.]] 
print(vec1_rot) # [0. 1. 0.]