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Python 3
Most common error that everyone is getting right now when trying to use futurize is failed to create process. If you are having this issue with futurize, please reinstall futurize. This can be done by uninstalling and installing it again using the following steps.
1. Python -m pip uninstall future
2. Python -m pip install future
From January 1, 2020 Python 2 is no longer supported. Therefore, from cycle 2020/01 (28th April 2020), IBEX will move to Python 3 only. Mantid is also migrating to Python 3 on the same timescale.
The materials used for Python 2 to 3 migration workshop can be found here: Workshop slides
The material is trimmed down to only target python 2 to 3 migration for IBEX users.
Note: This guide is not for converting your script from python 2 to 3. This is only for making your script compatible with 2 and 3.
The main reason for migrating is that Python 2 is no longer supported by its creators. Python 3 also has implemented many useful features and its support community is growing making it easier for users to learn Python 3.
Under python 3, the mechanism by which instrument scripts are imported has changed.
For instruments with single-file inst modules, we have migrated your scripts from
C:\Instrument\Settings\config\[MACHINE_NAME]\Python\inst\xxx_routines.py
to
C:\Instrument\Settings\config\[MACHINE_NAME]\Python\inst.py.
No further changes are required in this case - all new functions added to inst.py will be available in the inst module after doing import importlib;importlib.reload(inst) in the python scripting console.
For instruments with multi-file inst modules, your instrument scripts are still in the same location as before, which is:
C:\Instrument\Settings\config\[MACHINE_NAME]\Python\inst\
However, when adding new functions, they will additionally need to be imported into
C:\Instrument\Settings\config\[MACHINE_NAME]\Python\inst\__init__.py
before they are available in inst. As before, you will still need to perform import importlib;importlib.reload(inst) in the scripting console to be able to use these new functions.
This change has been made because our previous approach (which attempted to emulate from * import *) is increasingly difficult to maintain in python 3, and has caused confusion in a number of instances due to functions accidentally overwriting previously defined functions of the same name.
You can learn more about the structure of python modules at https://docs.python.org/3/tutorial/modules.html#packages
Python 3 introduces a number of changes, but the 3 main changes you need to be aware of are:
- changes to the syntax of print statements
- behaviour of the division operator
- changes to text and binary data
There are some other changes. We've listed the most common ones below. If your scripts rely on behaviour that changes in Python 3, you need to update your scripts to the new Python 3 behaviour.
In Python 3, the print statement becomes a function. Therefore, you need to pass the string you wish to print in parentheses. For example:
- in Python 2 you would write:
print "Hi this is Python 2" - in Python 3 you write:
print("Hi this is Python 3)
In Python 3, the division of two int values will result in float: for example: 5/2 will result in 2.5. If you want the division of two int values to result in an integer, use the // operator: for example 5//2 will result in a value of 2.
In Python 3 there are more escape sequences so make sure that any strings with escape characters are correct. To put a \ in a string you must either use \\ or place an r character before the string. Be especially careful of paths like "C:\instrument\setting\NDX.." where the \ are acting as escape characters this should become one of
r"C:\instrument\setting\NDX..""C:\\instrument\\setting\\NDX.."-
os.path.join("c:\\", "instrument", "setting" "NDX").
The handling of text and binary data changes in Python 2. This is one of the main reasons why Python 3 is not backwards compatible with Python 2. In Python 3, text and binary data are distinct types which users are not allowed to mix together. For example var = b"python" + u"three" is an illegal operation, whereas in Python 2 this was a permitted operation.
String literals such as var = "Python" are Unicode by default in Python 3, whereas in Python 2 they were of type bytes. Comparison between of type bytes and Unicode for e.g. b"test2" == u"test" would return true in Python 2 whereas in Python 3 it returns false.
Python 3 way of rounding is the standard of way of rounding decimals when it has resulted in a tie(.5). Python 3 will now round to the nearest even number, unlike Python 2 which rounds up to the next largest integer. For e.g. round(16.5) will result in 16 in Python 3 whereas in Python 2 it will result in 17.
Python 2 xrange is now equivalent to Python 3 range. range cannot be used as list object for e.g. range(0,10) will no longer return a list of [0,1...,9]. It can still be used in for loop for x in range(10). If you need a list you using range() you can still do list(range(0, 10)) which will then return a list.
The Future module eases the process of making Python 2 code compatible with Python 3 as well. The Workshop Slides provide an introduction to futurize.
To run futurize in more than one files you have to make sure that all the .py files you want to convert is in the same directory for e.g. C:\example\allPythonScripts all my scripts to be converted are in the folder allPythonScripts. Once you have collected the scripts you want to convert in a single directory, run the command futurize –w C:\example\allPythonScripts.
This will then convert all scripts present in allPythonScripts to python2/3 compatible script. It will also generate a file with extension .py.bak which is a backup file. If you require original python file then you can simply rename the file extension from .py.bak to .py. If you want to be careful about what futurize might do to your python file, running the command without -m flag futurize C:\example\allPythonScripts will only suggest you some changes without overwriting it. Please do make sure manually that changes made by futurize are valid.
Python 3 has disallowed implicit relative import and only the following two imports are allowed.