Python on z/OS – Helpful hints

This posts contains small snippets of useful information about using IBM Python on z/OS.

• Set up an alias for python3
• Creating a .py file is harder than it looks
• Displaying square brackets [] in your OMVS session
• How to edit source and get the brackets right
• What is installed?
• How to install software in an isolated z/OS environment
• What machine is this running on?
• Using struct.pack on z/OS

Setup an alias for python3

I set up an alias so I can type p3 or py instead of python3.

alias p3=”python3″
alias py=”python3″

Creating a .py file is harder than it looks

It was easy to create a .py file in Unix Services. It was hard to create a file which I could edit, would build and be compiled. For example I could execute a .py file. If I tried to compile it (as happens when you build it) I got

Compiling ‘/u/pymqi/mq2.py’…
*** Sorry: UnicodeDecodeError: ‘utf-8’ codec can’t decode byte 0xa2 in position 0: invalid start byte

I found a couple of ways of solving this problem

Use

touch myfile.py
chtag -tc ISO8859-1 myfile.py
oedit myfile.py

To undo this use IBM-1047.

Copy an existing file for example

cp /u/tmp/python/usr/lpp/IBM/cyp/v3r10/pyz/lib/python3.10/site-packages/pip/main.py my.py

Then edit my.py, remove all of the content and add in my content using cut and paste.

A different approach – useful when copying packages to z/OS was to FTP a .py file from Linux as BINARY then use

chtag -tc t ISO8859-1 mynew.py

So that z/OS recognises it as ASCII.

Displaying [] in your OMVS session

I could only get ISPF to display [] by using settings, and configuring terminal type to be 3278 (not 3278A as the documentation says).

The OMVS command has a CONVERT option that lets you specify a conversion
table for converting between code pages. The table you want to specify depends
on the code pages you are using in MVS and in the shell. For example, if you are
using code page IBM-037 in MVS and code page IBM-1047 in the shell, specify the
following when you enter the TSO OMVS command:
OMVS CONVERT((BPXFX111))

For example the program

a = {“a1″,2,”a3”}
b = [“a1″,2,”a3”]
print(a)
print(b)

With OMVS CONVERT((BPXFX111)) when you run it, you get

{‘a1’, 2, ‘a3’}
[‘a1’, 2, ‘a3’]

With OMVS you get

{‘a1’, 2, ‘a3’}
Ý’a1′, 2, ‘a3’¨

How to edit source and get the brackets right

The provided .py files format ok in ISPF when using US English 037. This is different to my normal code page of Bracket CP037 Modified.

With US English 037 in ISPF editor I get

a = {“a1″,2,”a3”}
b = [“a1″,2,”a3”]

With Bracket CP037 Modified – which works for normal C

a = {“a1″,2,”a3”}
b = Ý“a1″,2,”a3”¨

What is installed

python3 -m pip list

How to install Python software in an isolated environment

If your z/OS is connected to the internet, you can use python3 -m pip install ….
It is harder if your z/OS is isolated and does not have direct connectivity.

Download the software to your workstation

I used site https://pypi.org/, found the software I was interested in (eg wheel) and downloaded it to Linux.

Upload to z/OS

I FTPed the file to z/OS in binary, keeping the same name wheel-0.37.1-py2.py3-none-any.whl

Install the software

You can install this in a virtual environment, or on the system wide Python. The file system Python is on needs to be writeable.

To display the syntax of the install command

python3 -m pip install -help

When I tried to install it using my non privileged userid I got

-[31]ERROR: Could not install packages due to an OSError: [Errno 111] EDC5111I Permission denied.: ‘/u/.local’ Check the permissions.
-[0]

I had to install it using my IBMUSER id which had more authority ( and could change any file etc), or use the option –no-cache-dir .

The command was

python3 -m pip install /u/tmp/py/wheel-0.37.1-py2.py3-none-any.whl /u/tmp/py/wheel-0.37.1-py2.py3-none-any.whl
Looking in links: /u/tmp/py/wheel-0.37.1-py2.py3-none-any.whl
Processing /u/tmp/py/wheel-0.37.1-py2.py3-none-any.whl
Installing collected packages: wheel
Successfully installed wheel-0.37.1
-[33]WARNING: Running pip as the ‘root’ user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv-%5B0%5D

When installing other software I had to use options

• -f : search for pre-req software in this directory
• –no-cache-dir : because it tried to write to a read only cache
• –user : to install it in the virtual environment, not the system wide python.

Uninstall the software

python3 -m pip uninstall wheel

What machine is this running on ?

My z/OS is z/OS 2.4 on zPDT on Linux.

import platform
sys.path.append('./')
import pymqi
print("machine",platform.machine())
print("platform",platform.platform())
print("arch ",platform.architecture())
print("process ",platform.processor())
print("compiler",platform.python_compiler())
print("system ",platform.system())

gives

machine 1090
platform OS-390-27.00-1090-64bit
arch (’64bit’, ”)
process
compiler Clang 4.0.1 (tags/RELEASE_401/final)
system OS/390

Using struct.pack on z/OS

I wanted to understand what pack did on z/OS. See “format characters” in the documentation. For example ‘c’ is character, ‘L’ is unsigned long. Using a statement like print(“i”,struct.pack(“i”,1)) to format a number I got

b b’\x01′
h b’\x00\x01′
H b’\x00\x01′
i b’\x00\x00\x00\x01′
I b’\x00\x00\x00\x01′
l b’\x00\x00\x00\x00\x00\x00\x00\x01′
L b’\x00\x00\x00\x00\x00\x00\x00\x01′
q b’\x00\x00\x00\x00\x00\x00\x00\x01′
Q b’\x00\x00\x00\x00\x00\x00\x00\x01′
n b’\x00\x00\x00\x00\x00\x00\x00\x01′
N b’\x00\x00\x00\x00\x00\x00\x00\x01′
P b’\x00\x00\x00\x00\x00\x00\x00\x01′

I also noticed a “funny”

z = b’AB23′
print(“4sll” , struct.pack(“4sll”,z,2,1))

gave me

4sll b’AB23\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00\x00\x00\x00\x00\x00\x01′

The red text is from the long variable, the green text is the padding to make the long value on a long boundary (8).