Letter frequencies in Moby Dick

The following program produces a bar chart of letter frequencies in the English language, estimated by analysis of the text of Moby Dick (available as a free download from Project Gutenberg). The vertical bars are centered, and labelled by letter.

import numpy as np
import matplotlib.pyplot as plt

text_file = 'moby-dick.txt'

# Initialize the dictionary of letter counts: {'A': 0, 'B': 0, ...}
lcount = dict([(l, 0) for l in letters])

# Read in the text and count the letter occurences
for l in open(text_file).read():
        lcount[l.upper()] += 1
    except KeyError:
        # Ignore characters that are not letters
# The total number of letters
norm = sum(lcount.values())

fig = plt.figure()
ax = fig.add_subplot(111)
# The bar chart, with letters along the horizontal axis and the calculated
# letter frequencies as percentages as the bar height
x = range(26)
ax.bar(x, [lcount[l]/norm * 100 for l in letters], width=0.8,
       color='g', alpha=0.5, align='center')
ax.tick_params(axis='x', direction='out')
ax.set_xlim(-0.5, 25.5)
ax.set_ylabel('Letter frequency, %')

Letter frequencies in Moby Dick