In [12]:

from traitlets import default, HasTraits, Integer, Unicode
from traitlets.config import Configurable, Config

In [16]:

class MyClass(Configurable):
    s = Unicode('default', config=True, help="my s")
    i = Integer(5, config=True, help="an integer")
    notconfigurable = Float(1.5, help="This isn't configurable")

In [17]:

print(MyClass.class_config_rst_doc())

MyClass.i : Int
    Default: ``5``

    an integer

MyClass.s : Unicode
    Default: ``'default'``

    my s

In [19]:

c = MyClass(s='x')
c.s

Out[19]:

'x'

In [7]:

class MyClass2:
    def __init__(self, s='default', i=5):
        self.s = s
        self.i = 5

In [20]:

import socket


class MyClass3(Configurable):
    hostname = Unicode('something', help="my hostname")

    @default('hostname')
    def _hostname_default(self):
        return socket.gethostname()
    

In [21]:

MyClass3().hostname

Out[21]:

'k5.simula.no'

In [5]:

c.s = "some string"
c.s

Out[5]:

'some string'

In [6]:

c.s = 5

---------------------------------------------------------------------------
TraitError                                Traceback (most recent call last)
<ipython-input-6-a90974018a65> in <module>()
----> 1 c.s = 5

~/conda/lib/python3.6/site-packages/traitlets/traitlets.py in __set__(self, obj, value)
    583             raise TraitError('The "%s" trait is read-only.' % self.name)
    584         else:
--> 585             self.set(obj, value)
    586 
    587     def _validate(self, obj, value):

~/conda/lib/python3.6/site-packages/traitlets/traitlets.py in set(self, obj, value)
    557 
    558     def set(self, obj, value):
--> 559         new_value = self._validate(obj, value)
    560         try:
    561             old_value = obj._trait_values[self.name]

~/conda/lib/python3.6/site-packages/traitlets/traitlets.py in _validate(self, obj, value)
    589             return value
    590         if hasattr(self, 'validate'):
--> 591             value = self.validate(obj, value)
    592         if obj._cross_validation_lock is False:
    593             value = self._cross_validate(obj, value)

~/conda/lib/python3.6/site-packages/traitlets/traitlets.py in validate(self, obj, value)
   2052                 msg = "Could not decode {!r} for unicode trait '{}' of {} instance."
   2053                 raise TraitError(msg.format(value, self.name, class_of(obj)))
-> 2054         self.error(obj, value)
   2055 
   2056 

~/conda/lib/python3.6/site-packages/traitlets/traitlets.py in error(self, obj, value)
    623             e = "The '%s' trait must be %s, but a value of %r was specified." \
    624                 % (self.name, self.info(), repr_type(value))
--> 625         raise TraitError(e)
    626 
    627     def get_metadata(self, key, default=None):

TraitError: The 's' trait of a MyClass instance must be a unicode string, but a value of 5 <class 'int'> was specified.

In [28]:

import argparse

parser = argparse.ArgumentParser()
parser.add_argument('-v', dest='verbose', action='store_true')
parser.add_argument('file', type=str, help="a file")
parser.parse_args()

usage: ipykernel_launcher.py [-h] [-v] file
ipykernel_launcher.py: error: unrecognized arguments: -f

An exception has occurred, use %tb to see the full traceback.

SystemExit: 2

/Users/benjaminrk/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py:2971: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
  warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)

In [25]:

sys.argv

Out[25]:

['/Users/benjaminrk/conda/lib/python3.6/site-packages/ipykernel_launcher.py',
 '-f',
 '/Users/benjaminrk/Library/Jupyter/runtime/kernel-529512a8-9a53-454d-93b3-b512fa5f95d1.json']

In [30]:

parser.parse_args(['myfile'])

Out[30]:

Namespace(file='myfile', verbose=False)

In [31]:

parser.parse_args(["-v", 'myfile'])

Out[31]:

Namespace(file='myfile', verbose=True)

In [35]:

!python /Users/benjaminrk/dev/ip/scripts/showargs.py -v myfile has spaces

['/Users/benjaminrk/dev/ip/scripts/showargs.py', '-v', 'myfile', 'has', 'spaces']

In [34]:

!python /Users/benjaminrk/dev/ip/scripts/showargs.py -v "myfile has spaces"

['/Users/benjaminrk/dev/ip/scripts/showargs.py', '-v', 'myfile has spaces']

In [36]:

sys.argv

Out[36]:

['/Users/benjaminrk/conda/lib/python3.6/site-packages/ipykernel_launcher.py',
 '-f',
 '/Users/benjaminrk/Library/Jupyter/runtime/kernel-529512a8-9a53-454d-93b3-b512fa5f95d1.json']

In [40]:

def main(argv=None):
    print(parser.parse_args(argv))

In [42]:

main()

usage: ipykernel_launcher.py [-h] [-v] file
ipykernel_launcher.py: error: unrecognized arguments: -f

An exception has occurred, use %tb to see the full traceback.

SystemExit: 2

/Users/benjaminrk/conda/lib/python3.6/site-packages/IPython/core/interactiveshell.py:2971: UserWarning: To exit: use 'exit', 'quit', or Ctrl-D.
  warn("To exit: use 'exit', 'quit', or Ctrl-D.", stacklevel=1)

In [45]:

def find_six(seq):
    for i, item in enumerate(seq):
        if item == 6:
            print(f"Found 6 at index {i}")
            break
    else:
        print("Never found 6!")

find_six([1, 2, 6, 5])

Found 6 at index 2
Never found 6!

In [44]:

find_six([1, 2, 3])

Never found 6!

In [50]:

from subprocess import Popen, PIPE, STDOUT

p = Popen(['echo', 'hi']) #, stdout=PIPE)
p.wait()
type(p.stdout)

Out[50]:

NoneType

In [ ]: