How to correctly code vectorized function entries in Python 2

问题

So I had played around some code I found online dealing with optimization using Python 3. Modified, it rendered a plot like this

Now I'm using Python 2, and the * is not being processed. I believe the issue is the Python iteration, but I'm not getting any results when following the parenthesis trick suggested in this post. Here is the entire code:

%matplotlib inline

import matplotlib.pyplot as plt
import pylab as pylab
import autograd.numpy as np

from mpl_toolkits.mplot3d import Axes3D
from matplotlib.colors import LogNorm
from matplotlib import animation
from IPython.display import HTML

from autograd import elementwise_grad, value_and_grad
from scipy.optimize import minimize
from collections import defaultdict
from itertools import izip_longest
from functools import partial

f  = lambda x, y: 10*np.cos(1*x) * 15*np.sin(1/2*y) + 150
xmin, xmax, xstep = -4.5, 4.5, .2
ymin, ymax, ystep = -4.5, 4.5, .2

x, y = np.meshgrid(np.arange(xmin, xmax + xstep, xstep), np.arange(ymin, ymax + ystep, ystep))
z = f(x, y)

minima = np.array([np.pi, np.pi])
minima_ = minima.reshape(-1, 1)

fig = plt.figure(figsize=(8, 5))
ax = plt.axes(projection='3d', elev=50, azim=-50)
ax.plot_surface(x, y, z, norm=LogNorm(), rstride=1, cstride=1, 
                edgecolor='none', alpha=.8, cmap=plt.cm.jet)
ax.plot(*minima_, f(*minima_), 'o', markersize=4, color='w')

ax.set_xlabel('$x$')
ax.set_ylabel('$y$')
ax.set_zlabel('$z$')

ax.set_xlim((xmin, xmax))
ax.set_ylim((ymin, ymax))

plt.show()

and the error message:

  File "<ipython-input-5-3b03e44c1cac>", line 31
    ax.plot(*minima_, f(*minima_), 'o', markersize=4, color='w')
SyntaxError: only named arguments may follow *expression

回答1:

Consider assigning both minima_ values by index. Below is compliant in both python 2 and 3:

a,b = minima_[0], minima_[1]                        # TO ADD
ax.plot(a,b, f(a,b), 'o', markersize=4, color='w')  # TO REPLACE

来源：https://stackoverflow.com/questions/44478341/how-to-correctly-code-vectorized-function-entries-in-python-2