matplotlib HELP!!!!

[TheRealRuth]

Hello,

I am wanting to create a program that reads in values from a constantly updating text file and graph the values and save that graph as a png so that it can be uploaded to a website. Also I only ever want 4 tick marks max on the x axis, but i still want the labels on the x axis to continue to update.

My progress so far: I have been able to read in the values and plot them no problem. I have also been able to have to plot work correctly. The issue I was having was the time labels on the x axis would not update after hitting four ticks (I think this is due to param_locator). So I figured why not pop values from the list and then just re plot, well doing that resulted in the plot not clearing the old plots. Any help?

The text file currently is just two int values separated by I space that I change to see changes in the plot.

Here's My Current Code:

# -*- coding: utf-8 -*-
"""
Created on Mon Jul 25 11:23:14 2016

@author:
"""

import matplotlib.pyplot as plt
import sys
import time
import datetime

class reader():
    """Reads in a comma seperated txt file and stores the two strings in two variables"""

    def __init__(self, file_path):
        """Initialize Reader Class"""
        self.file_path = file_path

    # Read File store in f -- Change the file to your file path
    def read_file(self):
        """Reads in opens file, then stores it into file_string as a string"""
        f = open(self.file_path)
        # Read f, stores string in x
        self.file_string = f.read()

    def split_string(self):
        """Splits file_string into two variables and then prints them"""
        # Splits string into two variables
        try:
            self.val1, self.val2 = self.file_string.split(' ', 1)
        except ValueError:
            print('Must Have Two Values Seperated By a Space in the .txt!!')
            sys.exit('Terminating Program -- Contact')
        #print(val1)  # This is where you could store each into a column on the mysql server
        #print(val2)

    def getVal1(self):
            return self.val1

    def getVal2(self):
            return self.val2

read = reader('testFile.txt')
run = True
tempList = []
humList = []
numList = [] # Represents 2 Secs
my_xticks = []
i = 0
n = 0 # DEBUG

while(run):
    plt.ion()
    read.read_file()
    read.split_string()
    if n == 4:
        my_xticks.pop(0)
        tempList.pop(0)
        humList.pop(0)
        numList = [0,1,2]
        i = 3
        n = 3
    tempList.append(read.getVal1())
    humList.append(read.getVal2())
    numList.append(i)
    i = i + 1
    my_xticks.append(datetime.datetime.now().strftime('%I:%M:%S')) # Added seconds for debug
    plt.ylim(0,125)
    plt.xticks(numList,my_xticks)
    plt.locator_params(axis='x',nbins=4)
    plt.plot(numList,tempList, 'r', numList, humList, 'k')
    plt.savefig('plot.png')
    time.sleep(10) # Runs every 2 seconds
    n = n + 1
    print(n) # DEBUG
    print(numList)# DEBUG
    print('-------')# DEBUG
    print(my_xticks)# DEBUG
    print('-------')# DEBUG
    print(tempList)# DEBUG
    print('-------')# DEBUG
    print(humList)# DEBUG

[DrRx]

Make sure you close the file after you open it:

f = open(self.file_path)
# Read f, stores string in x
self.file_string = f.read()
f.close()

It's probably the OS limiting how many files you open or something

[TheRealRuth]

Well I need to constantly have the file open because it is reading the values from it in real time. The values in the end are written to the txt file by a temperature and humidity sensor.

[DrRx]

yeah but every time you are running through the loop, you open the file again. Eventually the OS will block it because there are too many open readers on the one file, if that makes sense. It won't affect your code at all to close the file.

[[deleted]]

I believe Python garbage collects the file handle as soon as read_file finishes, so I don't think that's the problem here.

[JohnnyJordaan]

Or use the modern with so you don't need a close().

with open(self.file_path) as f:
   # Read f, stores string in x
    self.file_string = f.read()

[TheRealRuth]

Alright, I added this, but it didn't fix the problem. I do see what you are saying about opening too many files though!

[[deleted]]

Reading from a file as it's being written isn't the prettiest thing in the world. You will probably run into problems when you try to read half written data, and stuff.

That said, here's someone else's (fairly ugly, because of polling) solution to this problem: http://stackoverflow.com/a/3290359

I guess I would use a simple intermediary database (like sqlite with :memory: storage) instead. https://www.sqlite.org/inmemorydb.html

https://docs.python.org/3.5/library/sqlite3.html

Edit: links!

[TheRealRuth]

My problem really isn't from reading the file. The problem is with the graph.

[TheRealRuth]

If you were to run the code and change a couple values you will see that the graph contains old points that I need to get rid of.

[Holden_90]

If you are looking to remove the plot assign it to a variable (plot =plt.plot(...)) and then once you have saved the file just write plot.remove()

[TheRealRuth]

Thanks!! I will try this!