Tracking Frequency in Python: Part I

Joaquín Menchaca (智裕)

May 10, 2019·2 min read

In many operations oriented roles, often times you need to write some scripts for automation. One common type of chore tracking the frequency of something. A typical problem will be to process text from a file, count the occurrence of some event, and then output a small report.

In this series, I will present the small coding challenge, and then provide some solutions using Python.

The Problem

Print the shell and number of users that use that shell with a local copy of /etc/passwd file. For this we’ll create a frequency hash, or dict in Python.

The Data

Here’s the local passwd file used for this exercise:

The Output

The output given the report given the data from above would have these counts:

Shell Summary Report:
==================================================
Shell               # of Users
-----------------   ------------
/bin/bash             3 users
/bin/false            7 users
/bin/sync             1 users
/usr/sbin/nologin    17 users

The Code

Here’s the boiler plate getting started code used for all the solutions. You can embed your solution in the middle of this. For the frequency hash, we’ll use a dict data structure called counts.

Python 3 has its own method to format strings using format() method, and similar other languages Python has a repetition operator *.

In Python, you can iterate through not only lists, but also dictionaries:

for item in list:
  print(item)for key, value in dictionary.items():
  print("{}:{}".format(key, value))

You can also sort a dictionaries by its keys with sorted(dictionary.items()).

Conclusion

In this article I only wanted to present the problem. In a follow-up articles (two parts), I’ll show ways to solve this with collection loop (for), lambda, and comprehension.

Some takeaways:

• creating an empty dictionary, e.g. newdict = {}
• formatted output with print(string.format())
• repetition operator *
• enumerating and sorting a dictionary
• the in operator