Subprocess - get only first few lines of stdout

[snippsat]

How did you know/decide to use decode('utf-8'), and not 'ascii' for example?

Python 3 represents strings as Unicode,and will not take in data without encoding(will be bytes string if try).
If have bytes,we can decode them to a Unicode string using UTF-8.

>>> b = b'hello'
>>> type(b)
<class 'bytes'>
>>> c = b.decode('utf-8') # Just b.decode() will do the same
>>> c
'hello'
>>> type(c)
<class 'str'>

Unicode was one biggest changes moving from Python 2 to Python 3.
Python 3 has UTF-8 as default encoding,Python 2 had ASCII as default encoding.