How to use python coverage inside the code

Question

I want to capture the coverage from inside the code. I tried below one but getting error. Referred to below link for coverage API. https://coverage.readthedocs.io/en/v4.5.x/api.html#api

import os
import pandas as pd
import sys
import requests
import xml.etree.ElementTree as ET
from xml.dom import minidom
import coverage

cov = coverage.Coverage()
cov.start()

#actual code

cov.stop()
cov.save()

cov.html_report(directory='covhtml')

getting below errors

CoverageException                         Traceback (most recent call last)
<ipython-input-15-2047badbbd57> in <module>()
     48 cov.save()
     49 
---> 50 cov.html_report(directory='covhtml')

C:\Users\\Anaconda2\lib\site-packages\coverage\control.pyc in html_report(self, morfs, directory, ignore_errors, omit, include, extra_css, title, skip_covered)
   1093             )
   1094         reporter = HtmlReporter(self, self.config)
-> 1095         return reporter.report(morfs)
   1096 
   1097     def xml_report(

C:\Users\\Anaconda2\lib\site-packages\coverage\html.pyc in report(self, morfs)
    137 
    138         # Process all the files.
--> 139         self.report_files(self.html_file, morfs, self.config.html_dir)
    140 
    141         if not self.all_files_nums:

C:\Users\\Anaconda2\lib\site-packages\coverage\report.pyc in report_files(self, report_fn, morfs, directory)
     81 
     82         if not file_reporters:
---> 83             raise CoverageException("No data to report.")
     84 
     85         self.directory = directory

CoverageException: No data to report.

Answer 1

If you wrap whatever you have for #actual code in a function, then it will work. Here's a (minimalish) example:

import coverage

def test_it(x):
    return x + 1

cov = coverage.Coverage()
cov.start()

test_it(123)

cov.stop()
cov.save()

cov.html_report(directory='covhtml')

However, if you would replace test_it(123) by just doing some inline statement (like x = 123; x += 1; print(x)), then the coverage module will fail.

It's well hidden, but the docs do explain this behavior:

start()

Start measuring code coverage.

Coverage measurement only occurs in functions called after start() is invoked. Statements in the same scope as start() won’t be measured.

Once you invoke start(), you must also call stop() eventually, or your process might not shut down cleanly.

Emphasis my own, here's the link: https://coverage.readthedocs.io/en/v4.5.x/api_coverage.html#coverage.Coverage.start