Understanding matplotlib xticks syntax

Question

I am reading a book and I came across this code:

import matplotlib.pyplot as plt
plt.scatter(x,y)
plt.title("Web traffic over the last month")
plt.xlabel("Time")
plt.ylabel("Hits/hour")
plt.xticks([w*7*24 for w in range(10)], 
  ['week %i'%w for w in range(10)])
plt.autoscale(tight=True)
plt.grid()
plt.show()

For context, x is an array of integers corresponding to an hour. y is an array of "hits" (from users to a website) in that particular hour.

I understand that the code accumulates all the hours so that it can display them in a week, but could someone please explain what these functions do? My goal is to understand all the syntax of this line:

plt.xticks([w*7*24 for w in range(10)], 
  ['week %i'%w for w in range(10)])

Specifically:

• What is range?

This is what gets generated:

Here is sample data for additional context:

1   2272
2   nan
3   1386
4   1365
5   1488
6   1337
7   1883
8   2283
9   1335
10  1025
11  1139
12  1477
13  1203
14  1311
15  1299
16  1494
17  1159
18  1365
19  1272
20  1246
21  1071
22  1876
23  nan
24  1410
25  925
26  1533
27  2104
28  2113
29  1993
30  1045

Answer 1

range is a function in python2 which makes a list for the argument given to it:

range(5) -> [0,1,2,3,4]
range(1,5) -> [1, 2, 3, 4]

in general range(lower_index, upper_index+1) will generate a list equivalent to [ lower_index, upper_index] in python2,

you can use xrange for better performance ( as it's uses lazy evaluation, calculating when it is needed) or range in python3 will do the work as xrange in python2.

now for the line:

plt.xticks([w*24*7 for w in range(10)],['week %i'%w for w in range(10)])

actually xticks is the interval for your x axis ticks or measurement, so as your level of measurement is in hours so it is better to tick for each hour in a week (i.e. 7 days * 24 hours) for the week's in the data set, and the second list comprehension put's the label's for that one week interval( week 0, week 1 .....),

one point to notice is that actually the data set you have used from the book have 748 rows so approximately (748/(24*7)) = 4.45 weeks ,,

so you really can plot the graph using range(5), the reason the output plot is scaled to week0 - week4 is because of the line plt.autoscale(tight=True), well without plt.autoscale the plot would have shown something like this.

hope it helps.