Function of a line of code

Question

For the following codes (which is used to generate a graph in IPython), what does if k in [0, len(n_trials) - 1] else None do?

%matplotlib inline
from IPython.core.pylabtools import figsize
import numpy as np
from matplotlib import pyplot as plt
#total figure size
figsize(11, 9)

import scipy.stats as stats

dist = stats.beta
n_trials = [0, 1, 2, 3, 4, 5, 8, 15, 50, 500]
data = stats.bernoulli.rvs(0.5, size=n_trials[-1])
x = np.linspace(0, 1, 100)

# For the already prepared, I'm using Binomial's conj. prior.
for k, N in enumerate(n_trials):
    sx = plt.subplot(len(n_trials) / 2, 2, k + 1)
    plt.xlabel("$p$, probability of heads") \
        if k in [0, len(n_trials) - 1] else None
    #Make the y label not appeared
    plt.setp(sx.get_yticklabels(), visible=False)
    heads = data[:N].sum()
    y = dist.pdf(x, 1 + heads, 1 + N - heads)
    plt.plot(x, y, label="observe %d tosses,\n %d heads" % (N, heads))
    plt.fill_between(x, 0, y, color="#348ABD", alpha=0.4)
    plt.vlines(0.5, 0, 4, color="k", linestyles="--", lw=1)

    leg = plt.legend()
    leg.get_frame().set_alpha(0.4)
    plt.autoscale(tight=True)


plt.suptitle("Bayesian updating of posterior probabilities",
             y=1.02,
             fontsize=14)

plt.tight_layout()

the `\\` at the end the previous line tells you that this is a continuation of that line. — Steve Lorimer, Aug 08 '14 at 06:26
That's a really weird way to write that code. It doesn't even save lines. — user2357112 supports Monica, Aug 08 '14 at 06:27

score 5 · Answer 1 · edited May 23 '17 at 10:33

5

That code is misleading in a number of ways. As pointed out in the comments, the line you're asking about is a continuation of the previous line, because of the escaping backslash. It becomes:

plt.xlabel("$p$, probability of heads") if k in [0, len(n_trials) - 1] else None

Which is just a convoluted way of writing:

if k == 0 or k == len(n_trials) - 1:
    plt.xlabel("$p$, probability of heads")

The syntax 'True' if condition else 'False' is Python's version of the ternary operator, but there is no reason to use it in this case.

edited May 23 '17 at 10:33

Community

1
1

answered Aug 08 '14 at 06:24

grc

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Urgh, the pythonic way! I think what your equivalent line is far more readable! – Steve Lorimer Aug 08 '14 at 06:27
5

@SteveLorimer -- What do you mean by "pythonic"? This way *is* the pythonic way to write it. The original code is just silly ... – mgilson Aug 08 '14 at 06:29
I wonder if the author of this code is normally a Ruby programmer? That syntax would be much more idiomatic in Ruby. – Daniel Roseman Aug 08 '14 at 09:06

Function of a line of code

1 Answers1