如何将一行 python 代码分配给变量

Question

I am plotting in python doing something like this:

plt.plot(xval_a_target, q_prof_target, label=r"target", color=target_color, ls=target_style, linewidth=lwidth)

I am creating a lot of different plots this way and would like to assign the latter part to a variable:

target_plot_style = """label=r"target", color=target_color, ls=target_style, linewidth=lwidth"""

In order to shorten the plot line to: plt.plot(xval_a_target, q_prof_target, eval(target_plot_style) , I tried it with eval and exec but it does not work. Is there a simple way to do this?

Answer 1

You can use a dict to hold those values:

kwargs = dict(label=r"target", color=target_color, ls=target_style, linewidth=lwidth)

And then apply them to the function call:

plt.plot(xval_a_target, q_prof_target, **kwargs)

Or you use partial to create a partially applied function:

from functools import partial

p = partial(plt.plot, label=r"target", color=target_color, ls=target_style, linewidth=lwidth)
p(xval_a_target, q_prof_target)

Or you create a function:

def p(xval_a_target, q_prof_target):
    return plt.plot(xval_a_target, q_prof_target, label=r"target", color=target_color, ls=target_style, linewidth=lwidth)

Don't think in terms of creating source code and eval ing it on the fly.

Answer 2

So essentially you want to have the process a bit more standardized.

There are two proper ways to do so:

1. Save the parameters you want to pass additionally into a dict and pass that dict when calling:

    target_plot_style = dict(label=r"target", color=target_color, ls=target_style, linewidth=lwidth) plt.plot(xval_a_target, q_prof_target, **target_plot_style)

2. Create a wrapper for this type of plots:

    special_plot = lambda x, y: plt.plot(xval_a_target, q_prof_target, label=r"target", color=target_color, ls=target_style, linewidth=lwidth) special_plot(xval_a_target, q_prof_target)

   or maybe

   def special_plot(x, y): return plt.plot(xval_a_target, q_prof_target, label=r"target", color=target_color, ls=target_style, linewidth=lwidth) special_plot(xval_a_target, q_prof_target)

Answer 3

It's example how to create dict with values you need. Then you can add **target_plot_stype to unpack dict.

def plt_plot(xval_a_target, q_prof_target, label, color, ls, linewidth):
    pass

if __name__ == "__main__":
    target_color = target_style = lwidth = xval_a_target = q_prof_target = 'value'
    target_plot_style = dict(label=r"target", color=target_color, ls=target_style, linewidth=lwidth)
    plt_plot(xval_a_target, q_prof_target, **target_plot_style)

Answer 4

Given that all your properties are in a list

for i in range(lwidth):

    plt.plot(xval_a_target[i], q_prof_target[i], label=r[i], color=target_color[i], ls=target_style[i], linewidth=lwidth[i])

Wouldn't this be valid enough?