gmtstrainplot python verion error

[xanthospap]

Describe the bug
Bug at program gmtstrainplot.sh
The bug is caused when bash calls python to compute/print computation results. Some of the calls
cause errors in Python3.x (e.g sclat=$(echo print ${south} + ${tmp_scrate} | python)). These lines
are ok for previous versions of Python.

To Reproduce
Steps to reproduce the behavior:

1. run command './gmtstrainplot.sh -jpg -vhor station_info.dat -psta -l -o output_vel'
   using Python 3.6
2. check for errors

"<stdin>", line 1
print 34 + 0.4

or

File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for -: 'builtin_function_or_method' and 'float'

Expected behavior
All of the lines just compute a bash variable (to be used later on)

Screenshots

Desktop (please complete the following information):

• OS: [Windows]
• Python: [3.6]
• GMT: [e.g. 5.2.1] -- irrelevant
• StrainTool: [v1.0-rc2.0]

Additional context
Bug reported by Varvara

[xanthospap]

Tried to fix this via computing all quantities with bc, but that is probably not an option. Python does complicated manipulations (like print(round(${T},-1)+10)); this is not possible with bc (at least not in less than a few lines).

[xanthospap]

Trying a new approach:

1. add a function in the script, to resolve system's python version (resolve_py_version())
2. make a function alias to python; this is called pythonc. If the system Python version is 3.x.x, then
   this function just collapses to alias pythonc="python -c". Else, if the version is 2.x.x, then the alias is
   python -c "from __future__ import print_function;.

Hence, now

1. When calling Python's print in the script, always use Python 3.x.x syntax
2. Instead of writing

python -c "print int((${south} + ${north})/2)"

we write

pythonc "print(int((${south} + ${north})/2))"

remember that is python 3.x print is a function, hence it must have parenthesis, print 5 is invalid, print(5) is ok!
Also, never use the piped version, aka echo print ${south} + ${tmp_scrate} | python