font = {"family" : "monospace",
        "size" : 12}
plt.rc("font", **font)
fig, ax1 = plt.subplots()
ax1.grid(ls="-", lw=.7)
ax1.tick_params(axis="both", labelsize=12)
ax1.set_xlabel("Date")
plt.setp(ax1.get_xticklabels(), rotation=90)
ax2 = ax1.twinx()
ax1.plot(date, p1, color='red', label="Param1")
ax2.plot(date, p2, color='blue', label="Param2", linestyle='--')
ax2.axhspan(29, 40, color='gray', alpha=0.4)
ax1.legend(loc="upper left", fontsize=10, ncol=1)
ax2.legend(loc="upper right", fontsize=10, ncol=1)
plt.savefig(plot_file, dpi=300, bbox_inches="tight")
plt.show()

 figure(figsize=(8, 6), dpi=80)

 ...
lns1 = ax.plot(time, Swdown, '-', label = 'Swdown')
lns2 = ax.plot(time, Rn, '-', label = 'Rn')
ax2 = ax.twinx()
lns3 = ax2.plot(time, temp, '-r', label = 'temp')
# added these three lines
lns = lns1+lns2+lns3
labs = [l.get_label() for l in lns]
ax.legend(lns, labs)

 plt.rcParams["font.size"] = "8"
fig = plt.figure(figsize=(19.20, 10.80), dpi=86)
a1 = fig.add_subplot()
a1.plot(date, p1, color='red', label="Param1")
a1.grid(ls="-", lw=.7)
a1.tick_params(axis="both")
a1.set_xlabel("Date")
a2 = a1.twinx()
a2.plot(date, p2, color='blue', label="Param2", linestyle='--')
fig.legend(labels=("P1", "P2"), loc="upper left")
plt.setp(a1.get_xticklabels(), rotation=90)
a2.axhspan(29, 40, color='gray', alpha=0.4)
plt.savefig(plot_file)
plt.show()

 #!/usr/bin/env python3
import csv
from matplotlib import pyplot as plt
# Plots
date = []
p1 = []
p2 = []
src_file = '1.csv'
with open(src_file, 'r') as f:
    reader = csv.reader(f, delimiter=';', quotechar='\'')
    for line in reader:
        month = int(line[0])
        if month in range(6,9):
            date.append("2021-{}-{}".format(line[0].zfill(2), line[1].zfill(2)))
            p1.append(int(line[3]))
            p2.append(int(line[2]))
plot_file = "plot-6-8.png"
fig = plt.figure(figsize=(19.20, 10.80), dpi=100)
plt.rcParams = {"font.size" : 12,
                "font.family" : "monospace"}
a1 = fig.add_subplot()
a1.plot(date, p1, color='red')
a1.grid(ls="-", lw=.7)
a1.tick_params(axis="both", length=10, pad=5)
a1.set_xlabel("Date")
a2 = a1.twinx()
a2.plot(date, p2, color='blue', linestyle='--')
fig.legend(labels=("P1", "P2"), loc="upper left")
plt.setp(a1.get_xticklabels(), rotation=90)
for label in a1.get_xaxis().get_ticklabels()[1::2]:
    label.set_visible(False)
plt.savefig(plot_file)
plt.show()