Plot of error in UILabel's vertical entering

uilabel-trace.py

#
# See http://stackoverflow.com/questions/30759598/how-does-uilabel-vertically-center-its-text/30910504#30910504
#

import re
import matplotlib.pyplot as pyplot

input = open("trace-output.txt").read()
entries = input.split("=====")

NUMBER_REGEX = "(\d+(?:\.\d+)?)"
RECT_REGEX = "{{%s, %s}, {%s, %s}}" % ((NUMBER_REGEX, ) * 4)
RE_BOUNDS = re.compile("drawTextInRect:" + RECT_REGEX)
RE_LABEL = re.compile("drawWithRect:" + RECT_REGEX)

def get_values(s):
    dict = {}
    match = RE_BOUNDS.search(s)
    if match is None:
        return None
    boundsHeight = float(match.group(4))
    match = RE_LABEL.search(s)
    if match is None:
        return None
    labelOffsetY = float(match.group(2))
    labelHeight = float(match.group(4))
    return (boundsHeight, labelOffsetY, labelHeight)
    
entries = [get_values(s) for s in entries]
entries = [x for x in entries if x is not None]
entries = sorted(set(entries), key=lambda tuple: tuple[2])

# entries is now a list of tuples of the form
# (boundsHeight, labelOffsetY, labelHeight)
# sorted by labelHeight

def calcOffset(boundsHeight, labelHeight):
    return (boundsHeight - labelHeight) / 2.0

calculatedOffsets = [calcOffset(bH, lH) for (bH, lY, lH) in entries]
appleOffsets = [lY for (bH, lY, lH) in entries]
diffs = [(a - b) for (a, b) in zip(appleOffsets, calculatedOffsets)]
labelHeights = [lH for (bH, lY, lH) in entries]

def plot(xlabel, x, ylabel, y):
    pyplot.plot(x, y, "ro")
    pyplot.xlabel(xlabel)
    pyplot.ylabel(ylabel)
    pyplot.show()

plot("label heights", labelHeights, "error", diffs)