Hangman('E', 'everything') ==> 'e_e_______'

Random tests consistently generate cases where at least two characters are not present. In fact, most of the test cases generate strings composed of underscores ('_') with random lengths.

Problems with typography and Markdown formatting:

• Use # heading not ###heading###
• No need to write headings in uppercase and followed by colon

The description should say what to do about corner cases:

• empty string given as input
• invalid locomotive position or multiple locomotives e.g. "_A__B"
• other characters in the input

I think the description should simply say:

You can assume that input will only contain valid trains (i.e. one locomotive followed by coaches).

A few semantics suggestions:
*delete the line 'The value is supposed to be an integer' and change the top line to be 'Your job is to return the amount of metal (an integer) needed...'
*change 'The coaches take 5 pieces of metal to make(for each) 'to 'The coaches take 5 pieces of metal each'
*I'd also suggest your two examples give different results - maybe something like 'D________' which is 48

nice easy problem

It is not clear from the description that the tests expect the output to be entirely lowercase regardless of the case of the input. I would suggest clarifying this in the description.

The trays are collor coded

collor -> color

No random tests

Traceback (most recent call last):
  File "tests.py", line 1, in <module>
    from solution import Hangman
ImportError: cannot import name 'Hangman' from 'solution' (/workspace/default/solution.py)

duplicate issue

use 3.8

Why is the function called bob ?

This series converges to e-1.

e = \sum_{k=0}^{\inf} 1/k! starting fom 0 (not 1).

Main issue:

Floats have limited precision, and are unable to exactly represent all needed values (only 18 different "e values" can be represented).
https://docs.codewars.com/authoring/kata/floating-point/
https://docs.python.org/3/tutorial/floatingpoint.html

It's better to use Fraction or Decimal.

Other issues:

• Floats should be compared with test.assert_approx_equals
• Floats should be summed with fsum, or at least from smaller to bigger.

Binary is just the number system with base 2. It is usually represented as a string in code, but thats not what makes it binary.