ポアソン分布でフィットしたい

\[P(x) = \exp(-\lambda)\frac{\lambda^{x}} {x!} \]
 1import pandas as pd
 2import numpy as np
 3import math
 4from scipy.optimize import curve_fit
 5
 6def poisson_function(x, amp, mu):
 7    """ポアソン分布
 8    """
 9    f = amp * math.exp(-mu) * mu**x / math.factorial(x)
10    return f
11
12def fix(data: pd.DataFrame):
13
14    func = poisson_function
15    x_data =
16    y_data =
17    p_init = [amp0, mu0]
18    popt, pcov = curve_fit(func, x_data, y_data, p_init)
19    perr = np.sqrt(np.diag(pcov))

リファレンス