使用循环绘制具有自定义线格式的大型数据集的强大解决方案

我试图从比较政治数据集中按年份绘制人口和国家数据。前任：

year    country   pop15_64   
1960  Australia    6296.50
1961  Australia    6428.60
1962  Australia    6571.50
1960        USA  107919.4
1961        USA  109048.6
1962        USA  111177.3

问题在于试图查看哪条线对应于哪个国家/地区。我尝试了许多不同的方法，最容易区分的似乎是将线条绘制为破折号。Ex（片段，不完整）：

df2.loc[df2['country'] == 'Cyprus'].plot(x='year', y='pop15_64', ax=ax, color='k')
df2.loc[df2['country'] == 'Czech Republic'].plot(x='year', y='pop15_64', ax=ax, color='g', dashes=[3, 3])

结果图：

但以上并不稳健。添加到数据集需要硬编码另一行，删除一个国家也是如此。这在数据上稳健地循环：

fig, ax = plt.subplots()
plt.xlabel('Year')
plt.ylabel('Population')
for countries in df2['country'].unique():
     df2[df2['country']==countries].plot.line(x='year',
                                              y='pop15_64',
                                              ax=ax,
                                              label=countries,
                                              title='Country Population by Year')

ax.legend(handlelength=5)
plt.show()

结果图：

...但我认为没有办法在不破坏循环的情况下自定义这些循环中的行。例如，这个：

for countries, x in df2['country'].unique():
     df2[df2['country']==countries].plot.line(x='year',
                                              y='pop15_64',
                                              ax=ax,
                                              dashes=[x+2, x],
                                              label=countries,
                                              title='Country Population by Year')

...results in a "ValueError: too many values to unpack (expected 2)"

What else I tried:
.groupby - couldn't get groupby and iterables to work together in one plot
iterables - had difficulty getting unique countries without losing the underlying data, still had line customization issues.

I admit that while I have experience in C, C++, and C#, I am a novice at python and more so with pandas. It requires a restructuring in how one thinks about problems. As a result, applying the many vaguely similar StackOverflow Q&A about custom lines and legends has not resulted in solutions like it might for someone with more experience. I hope someone knows an answer, and that this might help more than just me.

更新：在 Peter Leimbigler 的回答之后，我针对这个暂定解决方案修改了上述内容：

for i, countries in enumerate(df2['country'].unique()):
     df2[df2['country']==countries].plot.line(x='year',
                                              y='pop15_64',
                                              ax=ax,
                                              dashes=[3+i, i/2, abs(i-2), i/2],
                                              label=countries)