Tag: python

Python — dis

Found a cool method for testing the efficiency of different approaches to a python expression — dis disassembles the call and prints the component steps. Here, we see that there’s not much functional difference between “not a=b” and “a != b”.

Cyberark — Error Listing Accounts

I was getting an odd error from my attempt to list accounts in Cyberark — “Object reference not set to an instance of an object”. Searching the Internet yielded a lot of issues that weren’t my problem (ampersands in account names in an older version, issues with SSL {and, seriously, someone says disable SSL on the connection they use to retrieve passwords!?! And not just random someone, but RAND?!?}). My issue turned out to be that I was copy/pasting code and used requests.post instead of requests.get — attempting to POST to a GET URL generates this error too.

DEBUG:urllib3.connectionpool:Starting new HTTPS connection (1): cyberark.example.com:443
DEBUG:urllib3.connectionpool:https://cyberark.example.com:443 “POST /PasswordVault/API/auth/Cyberark/Logon HTTP/1.1” 200 182
Before request, header is {‘Content-Type’: ‘application/json’, ‘Authorization’: ‘5TQz5WVjYm5tMjBh5C00M5YyLT50MjYt5Tc2Y5I2ZDI5…AwMDA5MDA7’}
DEBUG:urllib3.connectionpool:Starting new HTTPS connection (1): cyberark.example.com:443
DEBUG:urllib3.connectionpool:https://cyberark.example.com:443 “POST /PasswordVault/api/Accounts?search=sample_account&searchType=contains HTTP/1.1” 500 97
{“ErrorCode”:”CAWS00001E”,”ErrorMessage”:”Object reference not set to an instance of an object.”} 500 Internal Server Error

Python Time-Expiring Cache

I needed to post information into a SharePoint Online list. There’s an auth header required to post data, but the authentication expires every couple of minutes. Obviously, I could just get a new auth string each time … but that’s terribly inefficient. I could also use what I had and refresh it when it fails … inelegant but effective. I wanted, instead, to have a value cached for a duration slightly less than the server-side expiry on the auth string. This decorator allows me to use the cached auth header string for some period of time and actually run the function that grabs the auth header string before the string is invalidated.

import functools
import time
from datetime import datetime

def timed_cache(iMaxAge, iMaxSize=128, boolTyped=False):
    # LRU cache decorator with expiry time
    # Args:
    #    iMaxAge: Seconds to live for cached results. 
    #    iMaxSize: Maximum cache size (see functools.lru_cache).
    #    boolTyped: Cache on distinct input types (see functools.lru_cache).
    def _decorator(fn):
        @functools.lru_cache(maxsize=iMaxSize, typed=boolTyped)
        def _new(*args, __time_salt, **kwargs):
            return fn(*args, **kwargs)

        def _wrapped(*args, **kwargs):
            return _new(*args, **kwargs, __time_salt=int(time.time() / iMaxAge))
        return _wrapped

    return _decorator

# Usage example -- 23 second cache expiry
def slow_function(iSleepTime: int):
    datetimeStart = datetime.now()
    return f"test started at {datetimeStart} and ended at at {datetime.now()}"

print(f"Start at {datetime.now()}")

for i in range(1, 50):
    if i % 5 is 0:
        print(f"sleeping 5 at {datetime.now()}")
        print(f"done sleeping at {datetime.now()}\n\n")

print(f"Ended at at {datetime.now()}")

Scraping Calendar Events

We’ve learned the value of engaging with local government — with few people involved in local proceedings, it’s pretty easy for a generally unpopular proposal to seem reasonable. And then we’re all stuck with the generally unpopular regulation. It is a pain, however, to keep manually adding the next Trustee meeting. And there’s no way I’m checking the website daily to find out about any emergency meetings.

Now I’m pulling the events from their Google calendar and creating new meeting items in my Exchange calendar:

  1. Register the app with Google to use the API
  2. Install exchangelib
  3. Copy config.sample to config.py and add personal information
  4. Create a ca.crt file with the CA signing key for your Exchange server (or remove the custom adapter if your server cert is signed by a public key)
  5. Run getCalendarEvents.py and follow the URL to authorize access to your calendar

I’ve tweaked the script to grab events from the school district’s calendar in SchoolPointe too. Now we know when there’s a school board meeting or dress-up day.

Extracting Waste Stream Collection Dates for the Netherlands

Yeah … mostly saving this for the regex search with a start and end flag that spans newlines because I don’t really need to know the date they collect each waste stream in the Netherlands. Although it’s cool that they’ve got five different waste streams to collect.

import requests
import re

strBaseURL = 'https://afvalkalender.waalre.nl/adres/<some component of your address in the Netherlands>' 
iTimeout = 600 
strHeader = {'User-Agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36'}

# Start and end flags for waste stream collection schedule content
START = '<ul id="ophaaldata" class="line">' 
END = '</ul>' 

page = requests.get(strBaseURL, timeout=iTimeout, headers=strHeader)
strContent = page.content
strContent = strContent.decode("utf-8")

result = re.search('{}(.*?){}'.format(START, END), strContent, re.DOTALL)
strCollectionDateSource = result.group(1)

resultWasteStreamData = re.findall('<li>(.*?)</li>', strCollectionDateSource, re.DOTALL)
for strWasteStreamRecord in resultWasteStreamData:
    listWasteStreamRecord = strWasteStreamRecord.split("\n")
    strDate = listWasteStreamRecord[3]
    strWasteType = listWasteStreamRecord[4]
    print("On {}, they collect {}".format(strDate.strip().replace('<i class="date">','').replace('</i>',''), strWasteType.strip().replace('<i>','').replace('</i>','')))

Python f-strings

I’m accustomed to using variables directly in strings — most of my scripting experience was with Bash, Perl, and PHP. It’s something I have to think about when I would write Java or C++ code, and it’s one of the few things that struck me as a step backward in Python. This is basically the advantage that kwargs have over args, except changing a string common where changing a function definition is pretty rare.

I’ve taken to using the arg identifier numbers in the print statement.

>>> first=”Lisa”
>>> last=”Rushworth”
>>> print(“Hi {0}, you are {0} {1}.”.format(first, last))
Hi Lisa, you are Lisa Rushworth.

This allows me to append a new variable to the format argument list and use it anywhere in the string
>>> salutation=”Hello”
>>> print(“{2} {0}, you are {0} {1}.”.format(first, last, salutation))
Hello Lisa, you are Lisa Rushworth.

Python 3 introduced f-strings, which go beyond the functionality I was missing. You *can* use variable names within the string:

>>> print(f”{salutation} {first}, you are {first} {last}”)
Hello Lisa, you are Lisa Rushworth

You can have multi-line strings — notice that newlines aren’t being magically added. If you *want* newlines, add \n!

>>> strString = (
… f”{salutation} {first}, ”
… f”You are {first} {last} ”
… f”And I have more ”
… f”data down here”
… )
>>> print(strString)
Hello Lisa, You are Lisa Rushworth And I have more data down here

But you can also perform operations:
>>> print(f”{2 ** 3}”)

And use the f-string in classes
>>> class MyThing:
… def __init__(self, thing1, thing2, thing3):
… self.thing1 = thing1
… self.thing2 = thing2
… self.age = thing3

… def __str__(self):
… return f”{self.thing1} has 2 {self.thing2} and 3 {self.age}.”

>>> thingSample = MyThing(“Something1”, “Something2”, “Something3″)
>>> print(f”{thingSample}”)
Something1 has 2 Something2 and 3 Something3.

What if you need to have a literal curly brace?
>>> print(f”Hi {first}, this output needs a {{curly brace}}”)
Hi Lisa, this output needs a {curly brace}

Two Approaches to Using PIP Through an Integrated Authenticated Proxy

The proxy at work uses integrated authentication. While BASIC auth prompts happily let you use a proxy of http://uid:pass@proxy:port, ours does not. There are two ways I’ve managed to use pip to install packages.

Proxied Proxy

The easiest approach is to use something that can handle the authenticated proxy, like Fiddler, as an intermediary. I do the same thing with perl’s PPM, docker pull … basically anywhere I’ve got to use a proxy that wants to pass through a proxy username.

Select Tools => Options to open the configuration dialog. Make sure you are handling SSL traffic — if not, check the box to “Capture HTTPS CONNECTs, “Decrypt HTTPS traffic”, and “Ignore server certificate errors” (it’s only unsafe if you don’t understand what you’re doing … don’t log into your bank account bouncing traffic through this config!)

On the “Connections” tab, check the port on which Fiddler is listening. If you cannot install Fiddler on the same box where you want to use pip, you’ll need to check off “Allow remote computers to connect” (and you won’t use localhost as the proxy hostname). Click OK, start capturing traffic (F12), and we’re ready to go.

Use the PIP command line to install the package but proxy the request through your Fiddler instance. In this example, Fiddler is installed on the local box and uses port 8888.

pip –trusted-host pypi.org –trusted-host files.pythonhosted.org –proxy http://localhost:8888 install SomePackage

This is nice because pip will automatically resolve dependencies. Not great if you’re not allowed to install your own software and cannot get Fiddler installed.

Dependency Nighmare

Back in the early days of Linux (think waaaay before package managers working against online repositories), we called this “dependency hell” — navigating dependency chains to get all of the required “stuff” on the box so you can install the thing you actually wanted.

Make a folder for all these wheels we’re going to end up downloading so it’s easy to clean up once we’re done. Search PyPi for the package you want. On the package page, select ‘Download Files’ and then download the whl

Use “pip install something.whl” to attempt installing it. If you’re lucky, you’ve got all the dependencies and the package will install. If you don’t have all of the dependencies, you’ll get an error telling you the first missing one. Go back to the pypi website & get that. Use “pip install somethingelse.whl” to install it and maybe get a dependency error here too. Once you get a dependency installed, try the package you want again. Got another error? Start downloading and installing again. Eventually, though, you’ll get all of the dependencies satisfied and be able to install the package you actually want.

Adding Python to Fedora Alternatives

Gimp installed Python 2.7). Which, of course, took over my system so nothing was using Python 3 anymore. We’ve used ‘alternatives’ to manage the Java installation, and I thought that might be a good solution in case I ever need to use Python 2

Add both Python versions to alternatives:

[lisa@fedora ~]# sudo alternatives –install /usr/bin/python python /usr/bin/python3.7 1
[lisa@fedora ~]# sudo alternatives –install /usr/bin/python python /usr/bin/python2.7 2

Select which one you want to use:

[lisa@fedora ~]# sudo alternatives –config python

There are 2 programs which provide ‘python’.

Selection Command
1 /usr/bin/python3.7
+ 2 /usr/bin/python2.7

Enter to keep the current selection[+], or type selection number: 1

And, of course, repeat the process for PIP:

[lisa@fedora ~]# sudo alternatives –install /usr/bin/pip pip /usr/bin/pip2.7 2
[lisa@fedora ~]# sudo alternatives –install /usr/bin/pip pip /usr/bin/pip3.7 1

[lisa@fedora ~]# sudo alternatives –config pip

List locally installed Python modules

I’ve been helping someone else get an Azure bot running on their system … which involves a lot of “what do I have that you don’t” … for which listing locally installed python modules is incredibly helpful.

python -c “import pkg_resources; print([(d.project_name, d.version) for d in pkg_resources.working_set])”


[lisa@cent6 ljr]# python -c “import pkg_resources; print([(d.project_name, d.version) for d in pkg_resources.working_set])”
[(‘scipy’, ‘1.2.0’), (‘scikit-learn’, ‘0.20.2’), (‘PyYAML’, ‘3.13’), (‘PyMySQL’, ‘0.9.3’), (‘pycares’, ‘2.4.0’), (‘numpy’, ‘1.16.0’), (‘multidict’, ‘4.5.2’), (‘Cython’, ‘0.29.4’), (‘coverage’, ‘4.5.2’), (‘aiohttp’, ‘3.0.9’), (‘yarl’, ‘1.3.0’), (‘wrapt’, ‘1.11.1’), (‘vcrpy’, ‘2.0.1’), (‘typing’, ‘3.6.6’), (‘sklearn’, ‘0.0’), (‘singledispatch’, ‘’), (‘sharepy’, ‘1.3.0’), (‘requests-toolbelt’, ‘0.9.1’), (‘requests-oauthlib’, ‘1.2.0’), (‘pytest’, ‘4.1.1’), (‘pytest-cov’, ‘2.6.1’), (‘pytest-asyncio’, ‘0.10.0’), (‘PyJWT’, ‘1.7.1’), (‘py’, ‘1.7.0’), (‘pluggy’, ‘0.8.1’), (‘oauthlib’, ‘3.0.1’), (‘nltk’, ‘3.4’), (‘msrest’, ‘0.4.29’), (‘more-itertools’, ‘5.0.0’), (‘isodate’, ‘0.6.0’), (‘ConfigArgParse’, ‘0.14.0’), (‘certifi’, ‘2018.11.29’), (‘botframework-connector’, ‘4.0.0a6’), (‘botbuilder-schema’, ‘4.0.0a6’), (‘botbuilder-azure’, ‘4.0.0a6’), (‘azure-devtools’, ‘1.1.1’), (‘azure-cosmos’, ‘3.0.0’), (‘attrs’, ‘18.2.0’), (‘atomicwrites’, ‘1.2.1’), (‘async-timeout’, ‘2.0.1’), (‘aiodns’, ‘1.2.0’), (‘botbuilder-core’, ‘4.0.0a6’), (‘systemd-python’, ‘234’), (‘smartcols’, ‘0.3.0’), (‘setools’, ‘4.1.1’), (‘rpm’, ‘’), (‘gpg’, ‘1.11.1’), (‘cryptography’, ‘2.3’), (‘cffi’, ‘1.11.5’), (‘urllib3’, ‘1.24.1’), (‘SSSDConfig’, ‘2.0.0’), (‘slip’, ‘0.6.4’), (‘slip.dbus’, ‘0.6.4’), (‘six’, ‘1.11.0’), (‘setuptools’, ‘40.4.3’), (‘sepolicy’, ‘1.1’), (‘requests’, ‘2.20.0’), (‘PySocks’, ‘1.6.8’), (‘pyparsing’, ‘2.2.0’), (‘pyOpenSSL’, ‘18.0.0’), (‘pykickstart’, ‘3.16’), (‘PyGObject’, ‘3.30.4’), (‘pycparser’, ‘2.14’), (‘ply’, ‘3.9’), (‘pip’, ‘18.1’), (‘ordered-set’, ‘2.0.2’), (‘isc’, ‘2.0’), (‘IPy’, ‘0.81’), (‘iotop’, ‘0.6’), (‘iniparse’, ‘0.4’), (‘idna’, ‘2.7’), (‘distro’, ‘1.3.0’), (‘decorator’, ‘4.3.0’), (‘chardet’, ‘3.0.4’), (‘asn1crypto’, ‘0.24.0’)]

Installing pycrypto On WIN10 with Visual Studio 2017

Yes, I know it’s old and no longer maintained … but it’s also what my function already uses, and I don’t want to take a few hours to get moved over to pycryptodome. You can install pycrypto on Windows 10 running Visual Studio 2017. But there’s a trick. Find the location of stdint.h in your VS installation.

Open x86_x64 Cross Tools Command Prompt For VS 2017


set CL=-FI"C:\Program Files (x86)\Microsoft Visual Studio\2017\Enterprise\VC\Tools\MSVC\14.14.26428\include\stdint.h"

where the bit in quotes is the path to your stdint.h (VS build version may differ, which will change the path).

Now, from within the Cross Tools Command Prompt, run:

pip install pycrypto

Voila — it installs: