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How to Upgrade Python 3.5 to 3.7 on Debian 9

sudo apt update
sudo apt install build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev wget
cd ~/Download
tar xf Python-3.7.3.tar.xz
cd ./Python-3.7.3 
./configure --enable-optimizations
make -j 8
sudo make install
sudo update-alternatives --install /usr/bin/python python /usr/local/bin/python3.7 10

Then to fix pip:

sudo ln -s /usr/share/pyshared/ /usr/local/lib/python3.7/site-packages/
sudo pip3 install --upgrade pip

How to Install Python 3.7 on Debian 9
sudo apt update
sudo apt install build-essential zlib1g-dev libncurses5-dev libgdbm-dev libnss3-dev libssl-dev libreadline-dev libffi-dev wget
cd ~/Download
curl -O
tar -xf Python-3.7.3.tar.xz
cd Python-3.7.3
./configure --enable-optimizations
nproc (see how many processors you have)
make -j 6
sudo make altinstall

Setup Python3 in Windows

Download and install Python for windows. If pip does not get installed with that, do the following:

Step 1: Download PIP
Before installing PIP, download the file: on
Open cmd
I had to add my pip and python folders to my path.
I had to copy/paste rename python.exe to python3.exe

Change python version system-wide

To change python version system-wide we can use update-alternatives command. Logged in as a root user, first list all available python alternatives:

update-alternatives --list python
update-alternatives: error: no alternatives for python

The above error message means that no python alternatives has been recognized by update-alternatives command. For this reason we need to update our alternatives table and include both python2.7 and python3.4:

sudo update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3.5 2
sudo update-alternatives --config python

Some error that I got

: No such file or directory

: No such file or directory

From the comments above it looks like you have dos line endings, and so the hashbang line is not properly processed.

Line ending style are not shown with :set list in Vim because that option is only used when reading/writing the file. In memory line endings are always that, line-endings. The line ending style used for a file is kept in a Vim per-file option, weirdly called fileformat.

To see/change the line ending style from Vim, you can use the following commands:

:set fileformat
:set ff

It will show dos or unix. You want unix, of course ;-).

To change it quickly you can save the file with:

:w ++ff=unix

or maybe more permenantly

tr -d '\r' < input.file > output.file

Edit config files

from configobj import ConfigObj
config = ConfigObj(r".bashrc")
global updated
updated = False

def update_me(key, value):
    if config[key] <> value:
        config[key] = value
        updated = True
        return updated

updated = update_me("alias ls", "ls --color=AUTO")
#updated = update_me("alias new", "new --color=AUTO")
updated = update_me("export EDITOR", "vim")

if updated == True:
    updated = False
    print("Config file updated...")

#print(config["alias ls"])


Install Python virtualenv.


sudo apt install python3 python3-venv
sudo apt install virtualenv python3-virtualenv

run virtualenv

python3 -m venv /path/to/virtual/environment
python3 -m venv ./python_venv
source my_project/bin/activate
source ./python_venv/bin/activate

Maybe at this point its a good idea to make sure that your python tools are up to date...

pip install --upgrade pip (do NOT run this on Python 2.6.8!)
pip install --upgrade pip==9.0.3 ( this should work on Python-2.6.8)
. . . . Do some stuff . . . . 

Code snip bits


is file/directory

import os.path
if os.path.exists(fname):
    # file exists as a object
if os.path.isfile(fname):
    # object is a file
if os.path.isdir(fname):
    # directory exists

Find all files and loop

import os

for root, dirnames, files in os.walk('/path/to/my/files/'):
    for filename in files:
        if filename.endswith(('.txt', '.sh', '.gif', '.png')):
            print("root: {}; filename: {}".format(root, filename) )

run external program

def exec_cmd(command):
    child = subprocess.Popen(command, shell = True, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
    stdout, stderr = child.communicate()
    rc = child.returncode
    return {"rc": rc, "stdout": stdout, "stderr": stderr


kill gracefully class

import signal
import time

class GracefulKiller:
  kill_now = False
  def __init__(self):
    signal.signal(signal.SIGINT, self.exit_gracefully)
    signal.signal(signal.SIGTERM, self.exit_gracefully)

  def exit_gracefully(self,signum, frame):
    self.kill_now = True

if __name__ == '__main__':
  killer = GracefulKiller()
  while True:
    print("doing something in a loop ...")
    if killer.kill_now:

  print("End of the program. I was killed gracefully")


word = Word(alphas)
num = Word(nums)
alpnum = Word(alphanums)
white = White(' ')
sub_word = Regex(r"[A-Za-z0-9_]*")
mac = Regex(r"([0-9A-Fa-f]{2}[:-]){5}([0-9A-Fa-f]{2})") + Suppress(restOfLine + lineEnd)
raw_ip = Combine(Word(nums, max=3) + "." + Word(nums, max=3) + "." + Word(nums, max=3) + "." + Word(nums, max=3))
# To find a word in a sentince
day = Keyword("day")
word = ~day + Word(alphas)  [So I see this as word is all words excusing day]
sentence = OneOrMore(word)
sentence_end_with_happy = sentence('first') + day + sentence('last') 
ret = sentence_end_with_happy.parseString("hi this is a nice day and everything is ok")
print ret['first']
print ret['last']
print ret


Use groups to get pyparsing to create a dictionary with labels.

my_line = Group((someword + Optional(Suppress(sentence) + second('second')) + Optional(otherword)('otherword')
          + Suppress(restOfLine + lineEnd) + restOfLine + lineEnd)))
section = bla + blabla + Optional(mac)('mac') + Optional(ZeroOrMore(my_line)('mline'))
## Loop through the results
for match in section.scanString(myvar):
    result = match[0]

remove a word from word

second = Keyword('secondary')
word2 = ~second + Word(alphas) 
sentence = OneOrMore(word2)   # So here we will have a "sentence" without the word 'secondary'


Literal('<') + SkipTo('>', include=True)


from tabulate import tabulate
result = exec_cmd('tcpdump -D')
if result['rc'] <> 0:
    log_error("Error from tcpdump. Please try again.")
    input_ints = result['stdout']
    table = []
    headers = (["Interface", "Status"])
    for lines in input_ints.strip().split('\n'):
        interfaces = lines.split('.', 1)[-1].split(' ', 1)[0]
        status = lines.split('.', 1)[-1].split(' ', 1)[1]
        # Build Table
        table.append(([interfaces, status]))
    print(tabulate(table, headers))


Use python runserver <ip>:<port>

For example,my IP is and I want to run django app on port 80,I have to do

[sudo] python runserver


on local pc

sudo apt install snapd (or snap is Debian Jessie)