如何使用 matplotlib 使用 .txt 文件中保存的数据绘制数据？

Question

I'm trying to load a graph using user input data, and my program is supposed to save the values in a txt file with a format that looks like this:

title

x-label

y-label

[a list of x-values]

[a list of y-values]

• each on their own line.

So what I have so far is:

def lagre():
    filnavn = input("Hvilket filnavn vil du lagre grafen din med? ")
    fil = open(filnavn, 'w', encoding="UTF-8")
    fil.write(str(label) + "\n")
    fil.write(str(x_akse) + "\n")
    fil.write(str(y_akse) + "\n")
    fil.write(str(x_liste) + "\n")
    fil.write(str(y_liste) + "\n")
    fil.close()
    return

    
def load():
    filnavn_open = input("Hvilken graf vil du åpne? ")
    f = open(filnavn_open, "r")
    print(f.read())
    vise()
    
def vise():
    plt.plot(x_liste, y_liste)
    plt.title(label)
    plt.xlabel(x_akse)
    plt.ylabel(y_akse)
    plt.grid(True)
    plt.show()

But it doesn't work, could anybody help?

Answer 1

You read the whole file by using f.read() . This means that calling f.readlines() afterwards returns an empty list. You can save the file content in a variable and then use this in your plots or just use f.readlines() .

Also you should close the file with f.close() . Alternatively you can use the with ... as statement.

So for example:

def load():
    filnavn_open = input("Which graph do you want to open?")
    with open(filnavn_open, "r") as f:
        filecontent=f.read()
    print(filecontent)
    
    # plots with filecontent

Answer 2

There are two problems in your approach:

1. the parameter size of the readline doesn't do what want to do, you can check out the documentation.

2. The x and y values need to be converted from str to list , the ast package does that.

Here is a working version:

import ast
from matplotlib import pyplot as plt

def load():
    filnavn_open = input("Which graph do you want to open? ")
    lines = ['title', 'xlabel', 'ylabel', 'x-values', 'y-values']
    with open(filnavn_open, "r") as f:
        g = {val: f.readline().strip() for val in lines}
    plt.plot(ast.literal_eval(g['x-values']), ast.literal_eval(g['y-values']))
    plt.title(g['title'])
    plt.xlabel(g['xlabel'])
    plt.ylabel(g['ylabel'])
    plt.grid(True)
    plt.show()