The performance effect of text overflow in a QPlainTextEdit with setMaximumBlockCount set.

qtextinsert.py

from pyface.qt import QtGui, QtCore
import time
import pandas
import numpy
from matplotlib import pyplot as plt

a = QtGui.QApplication.instance() or QtGui.QApplication([])

w = QtGui.QPlainTextEdit()
w.setMinimumSize(600, 400)
#w.setReadOnly(True)
w.show()

append_sizes = [100, 200, 500, 1000, 2000, 5000, 10000, 20000]
buffer_sizes = [100, 200, 500, 1000, 2000, 5000, 10000, 20000]

def setup(count):
    w.setPlainText('')
    # Comment next line to start from empty widget
    w.setPlainText('\n'.join(map(str, xrange(count))))
    w.setMaximumBlockCount(count)
    w.show()

def time_append(buffer_size, text_size):
    setup(buffer_size)
    text = '\n'.join(map(str, xrange(text_size)))
    
    t = time.time()
    # Uncomment next line to see effect of text overflow
    # w.setPlainText('')
    w.appendPlainText(text)
    t = time.time()-t
    print 'count: %s: text: %s time: %s' %(buffer_size, text_size, t)
    return t

def do_one(buffer_index, text_index):
    print buffer_index, text_index
    buffer_size = buffer_sizes[buffer_index]
    append_size = append_sizes[text_index]
    df[buffer_size][append_size] = time_append(buffer_size, append_size)
    text_index += 1
    if text_index == len(append_sizes):
        text_index = 0
        buffer_index += 1
        if buffer_index == len(buffer_sizes):
            do_plot()
            return
    QtCore.QTimer.singleShot(100, lambda:do_one(buffer_index, text_index))

def do_plot():
    print df
    for col in df:
        plt.loglog(df[col].index, df[col].values, '.-', label=str(df[col].name))
    plt.xlabel('Buffer Size')
    plt.ylabel('Time to Append')
    plt.legend(loc='best')
    plt.show()

def do_it():
    print 0,0
    do_one(0, 0)

df = pandas.DataFrame(numpy.zeros((len(buffer_sizes), len(append_sizes))),
                      index=append_sizes, columns=buffer_sizes)
QtCore.QTimer.singleShot(100, do_it)
a.exec_()