This module contains a lightweight library for creating command line programs, conz.
conz has following features:
- Simplifies working with pipes
- Provides methods for handling typical interactive scenarios
- Supports output colorization
- Provides tools for working with long-running tasks
- Controls output in interactive and non-interactive scenarios
- Manages signals (SIGINT and SIGPIPE)
Contents
You can install conz from PyPI using pip or easy_install:
pip install conz easy_install conz
A quick tour example can be found in examples/quicktour.py:
import conz
someval = True
cn = conz.Console(verbose=True)
cn.pstd('This goes to STDOUT')
cn.perr('This goes to STDERR')
cn.pverr(someval, 'This message is related to somevar')
cn.pstd(cn.color.green('This message is green'))
with cn.progress('Some long operation'):
import time
time.sleep(2)
data = cn.read('Type something in:')
cn.pstd('You typed in {}'.format(cn.color.yellow(data, style='italic')))
Because this library deals with terminal output a lot, we have to somehow tell when something is terminal output and when it is code. Because of this, we use lines to delimit console output. For example:
---------------------------------------------- I'm a sample output ----------------------------------------------
When output is to the STDERR, 'E' will be shown in the right corner.:
---------------------------------------------E I'm a sample error ----------------------------------------------
When user enters data, the Entered data will be followed by <Enter> and the
right corner will include the 'I' character (for 'interactive session'):
---------------------------------------------I Prompt: some data<Enter> ----------------------------------------------
When value is returned from user input, the value is printed right below the
output preceeded by ==>:
---------------------------------------------I Prompt: some data<Enter> ---------------------------------------------- ==> 'some data'
The conz package includes a class Console which is the only class you
will even need to work with. Simply import and instantiate it at the top of
your program.
import conz cn = conz.Console()
The Console() class is, for the most part, a wrapper around the print()
function (not print statement, so not compatible with versions of Python that
do not support this). It controls how print() is invoked and takes care of
some of the edge cases where it may malfunction.
The print() method on a Console object is a very simple wrapper around
Python's print() whic does nothing except pass it's positional and keywrod
arguments to the print() function. We will never use it directly, though,
as there are shortcuts for doing specific things with print().
To output to STDOUT, we use the pstd() method. It takes the same arguments
as print() function, with the exception of file keyword argument which
is set by this method and cannot be overridden.
cn.pstd('This always goes to STDOUT', end='...')
----------------------------------------------
This always goes to STDOUT
----------------------------------------------
To output to STDERR, we use the perr() method. As with pstd(), it
overrides the file argument for us.
cn.perr('Mayday, mayday!')
---------------------------------------------E
Mayday, mayday!
----------------------------------------------
The main difference between regular print() and pstd()/perr()
methods is that the latter will flush the STDOUT/STDERR after writing to it.
This can prvent weird issues in some edge cases.
There is a variant of perr() which prints a more structured message to
STDERR. The pverr() method takes a value and a message, and prints then in
VALUE: Message format.
path = '/foo/bar/baz.txt' cn.verr(path, 'not found') ---------------------------------------------E /foo/bar/baz.txt: not found ----------------------------------------------
A variant of pstd() is pverb(). It is exactly the same as pstd(),
except that it only outputs when verbose flag on the Console object is
True. This is useful for programs that need to differentiate between
interactive and non-interactive use (e.g., using in pipe vs invoking directly)
or wish to have a --verbose switch, etc.
cn.verbose = True
cn.pverb("I'm a talkative program")
----------------------------------------------
I'm a talkative program
----------------------------------------------
cn.verbose = False
cn.pverb("I'm a talkative program")
----------------------------------------------
----------------------------------------------
The verbose flag can be set either as an argument during instantiation, or
simply by setting the attribute as in the previous example.
The Console object also provides a outterm property which is False
when program is outputting to a pipe rather than the terminal:
if cn.outterm:
# give full output to the user
else:
# give a short output that can be parsed by a machine, etc
Before we start, note that this implementation is not cross-platform. If you need something with a bit more punch, you should look at colorama.
To colorize the output, both the conz module and Console class have a
color attribute, which provides methods for output colorization. Each piece
of text can have the following attributes:
- foreground color
- style
- background color
Foreground and background colors can be:
- black
- red
- green
- yellow
- blue
- purple (magenta)
- cyan
- white
Styles can be:
- bold
- italic
- underline
- blink
- reverse (inverts foreground and background colors)
Each of these colors have a method on the color attribute. Each color
method takes style and bg keyword arguments which set the style and
background color respectively. The color() method can be used to specify
colors dynamically. Here are some examples:
cn.color.red('This is red text')
cn.color.color('This is red text', color='red')
cn.color.blue('This is blue underlined text', style='underline')
cn.color.color('This is green on yellow', color='green', bg='yellow')
You can find an example script in examples/colors.py which prings all
possible combinations of various colors, styles, and backgrounds.
There are two types of input you can work with: interactive user input, and pipes.
To read the user input, use read() method. This method takes two optional
arguments. One is the prompt argument, which we use to set the prompt. It
is an empty string by default. The other argument is a data-cleaning function.
When you pass the clean argument, user input is passed through the function
before it is retuned. For example:
cn.read('Exit? [y/N] ', clean=lambda x: x.lower()[:1] == 'y')
---------------------------------------------I
Exit? [y/N] y<Enter>
----------------------------------------------
==> True
Note that this method uses raw_input() on Python 2.7.x and input() on
Python 3.x.
To work with pipes, we use the readpipe() method. This method reads from
the STDIN pipe one line at a time and returns an iterator that allows us to
iterate over the lines.
for l in cn.readpipe():
l = l.strip()
cn.pstd('Received: {}'.format())
Note that line-feed characters are not stripped from the output so it is up to us to strip it away.
When working with a large number of lines coming down the pipe, we may
sometimes need to work in batches, rather than one line at a time. The
chunk argument can be set to an integer value that specifies the number of
lines we want buffered before they are returned to us. When using chunks, the
lines are returned as a list of strings, rather than strings. The following
example will return pipe input in groups of 500:
for lines in cn.readpipe(500):
# do something with 500 lines
If we need to know whether input will come from a pipe or not, we can use the
interm property.
if cn.interm:
# possibly interactive version
else:
# we are on the receiving end of a pipe
So far we have looked at simpe user input. However in most cases, input is not
the only thing we want. We normally also need to show notes, validate the
input, construct menus, etc. The Console class provides three methods that
are useful for different scenarios.
You will find examples of code discussed here in examples/user_input.py and
examples/menu.py.
RVPL (pead validate print loop) is a loop in which some data is read from the
user, validated, and error message printed. This loop continues as long as data
is invalid. The rvpl() method is used to start such a loop.
At bare minimum, rvpl() is called with a prompt that should be shown to the
user.
cn.rvpl('Please enter your name:')
---------------------------------------------I
Please enter your name: My name<enter>
----------------------------------------------
==> 'My name'
Like read(), rvpl() also takes a clean argument, which is used to
control how the value is cleaned. In addition, it takes validator argument,
which is a function that validates the cleaned data. The default validator
simply makes sure the input is not an empty string.
For invalid input, error message is displayed:
cn.rvpl('Please enter your name:')
---------------------------------------------I
Please enter your name: <Enter>
Entered value is invalid
Please enter your name: Mike<Enter>
----------------------------------------------
==> 'Mike'
Error message can be customized using the error argument. If error
argument is is a callable, it will be called with entered value and it must
return the message to be shown.
valid_input = ('a', 'b', 'c')
error = lambda x: '{} is not one of the {}'.format(
x, ', '.join(valid_input))
validator = lambda x: x in valid_input
cn.rvpl('Type one of the first 3 characters of English alphabet:')
---------------------------------------------I
Type one of the first 3 characters of English alphabet: e<Enter>
e is not one of the a, b, c
Type one of the first 3 characters of English alphabet: b<Enter>
----------------------------------------------
==> 'b'
An intro message can be passed which is shown above the prompt. Unlinke the prompt itself, intro message is not repeated in the loop.
cn.rvpl('>', intro='Please enter your name:')
---------------------------------------------I
Please enter your name:
> <Enter>
Entered value is invalid
> Mike<Enter>
----------------------------------------------
==> 'Mike'
When requesting optional input, the strict validation can be turned off using
the strict argument. When this argument is False, then the loop exists
even when validation fails. The value returned when validation fails is
controlled by default argument, which defaults to None.
cn.rvpl('Please enter your name:', strict=False, default='Bob')
---------------------------------------------I
Please enter your name: <Enter>
----------------------------------------------
==> 'Bob'
The yesno() method provides a specialized version the RVPL limited to yes
and no answer, and returnin True or False.
cn.yesno('Are you all right?')
---------------------------------------------I
Are you all right? (y/n): y<Enter>
----------------------------------------------
==> True
The prompt passed to yesno() is automatically appended the '(y/n):' string.
The appearance of this string depends on the default value discussed further
below.
Since it is a wrapper around rvpl() it takes the same error and
intro arguments which behave the same way.
Although it takes the default argument like rvpl(), the behavior is
different. When default is None it automatically turns on strict
validation. The argument can also be either True or False, in which
case the default value is respectively 'yes' and 'no'.
cn.yesno('Are you all right?', default=True)
---------------------------------------------I
Are you all right? (Y/n): <Enter>
----------------------------------------------
==> True
cn.yesno('Are you all right?', default=False
---------------------------------------------I
Are you all right? (y/N): <Enter>
----------------------------------------------
==> False
Menu is another specialization of the RVPL, used for displaying menus. This is
facilitated by the menu() method.
This method has only one required argument, which is an iterable of menu choices. Each member of the iterable must be a two-tuple which holds the actual value as first member and the value's label as second. For example:
choices = (('f', 'foo'), ('b', 'bar'))
cn.menu(choices)
---------------------------------------------I
1) foo
2) bar
Please choose from the provided options: 1<Enter>
----------------------------------------------
==> 'f'
Almost all aspects of the menu can be customized. The prompt, error,
intro, strict and default behave the same way as in regular RVPL so
we will not discuss them in detail here.
Display of the menu items themselves is controlled by two arguments:
formatter and numerator.
numerator argument controls how the enumeration of the menu items is done.
It takes the number of menu items as its only argument, and must return a list
of strings to be used as options. For example:
choices = (('f', 'foo'), ('b', 'bar'))
numer = lambda n: ('abcd'[i] for i in range(n), numerator=numer)
cn.menu(choices)
---------------------------------------------I
a) foo
b) bar
Please choose from the provided options: a<Enter>
----------------------------------------------
==> 'f'
formatter takes the number of the item and item's label and must return a
formatted menu item. For example:
choices = (('f', 'foo'), ('b', 'bar'))
fmt = lambda n, lbl: '{} ({})'.format(lbl, n)
cn.menu(choices, formatter=fmt)
---------------------------------------------I
foo (1)
bar (2)
Please choose from the provided options: 1<Enter>
----------------------------------------------
==> 'f'
Progress is a more complex construct that we use to notify user of some activity that may take a while. Each progress has a start banner, which is printed before we begin, and two end banners, one for success and one for failure.
Before we can use the progress context manager, we must enable verbose mode.
cn.verbose = True
A progress is started using the progress() method, which is a context
manager.
with cn.progress("Let's get this show on the road"):
# do something
This is the simplest form. When an exception of any kind is triggered inside
the context, it is trapped, the failure banner is printed, and the
conz.ProgressAbrt exception is raised. (This exception is also available as
an attribute on Console objects for convenience.) If everything goes well,
then the success banner will be printed. With the previous code snippet, sucess
output may look like this:
---------------------------------------------- Let's get this show on the road...DONE ----------------------------------------------
And failure would look like this:
---------------------------------------------- Let's get this show on the road...FAIL ----------------------------------------------
The end banners can be customized by using the end and abrt arguments:
with cn.progress('Almost there', end='finally!', abrt='awww, bummer'):
# do something
The outputs would look like this:
---------------------------------------------- Almost there...finally! ----------------------------------------------
or:
---------------------------------------------- Almost there...awww, bummer ----------------------------------------------
The elipsis (three dots) can be customized using the sep argument:
with cn.progress('File check', sep=': '):
# do something
This results in:
---------------------------------------------- File check: DONE ----------------------------------------------
or:
---------------------------------------------- File check: FAIL ----------------------------------------------
By default, the progress context manager will trap any exception. This may or
may not make sense for a particular situation. This behavior can therefore be
customized using the excs argument, which takes a tuple of exception
classes that we are expecting. Passing exceptions explicitly like this allows
the context manager to propagate unhandled exceptions and reval subtle flaws in
our logic.
We can also specify a callback that runs each time an exception (other than
ProgressAbrt and ProgressOK are raised inside the context. This
callback is specified using onerror argument, and defaults to an error
handler that prints 'Program error: ERROR MESSAGE' to STDERR. For convenience,
the Console object has a error() method which creates such handlers.
By default, the tracebacks raised during progress is suppressed. To see the
full traceback, Console constructor takes a debug argument, which can
be set to True to prevent traceback suppression.
To create a handler, we call the error() method like so:
handler = cn.error('Ouch!', exit=1)
with cn.progress('Ouch progress', onerror=handler):
raise RuntimeError()
The above results in:
---------------------------------------------- Outch progress...FAIL Ouch! ----------------------------------------------
The message may have a {err} placeholder, which gets replaced by the string
representation of the exception that was raised in the block.
To completely suppress the error handler, simply pass it a function that does nothing.
with cn.progress('No ouch', onerror: lambda exc: None):
raise RuntimeError()
----------------------------------------------
No ouch...FAIL
----------------------------------------------
Note
Note that passing None as onerror value simply causes the default
error handler to be used instead.
The progress context manager returns a Progress object, which provides
methods for explicitly terminating the progress, and printing the progress
indicator. This object has end() and abrt() methods, which are called
to terminate with success and error status respectively. For example:
with cn.progress('Something') as prg:
if not success:
prg.abrt()
prg.end()
The end() and abrt() methods raise ProgressOK and ProgressAbrt
exceptions repsectively. We can suppress raising of the exceptions using
noraise argument and setting it to True. Both of the methods will use
the default end banners. We can also use any banner we want by passing it as
the first positional argument. This can be useful in cases where the end banner
should indicate different outcomes.
Note
Default banners are colorized (green for success, red for failure). Any
custom banners passed directly to end() and abrt() will not be
colorized, though.
The ProgressOK exception is not meant to be
handled by us in any way, and it's simply there to facilitate flow control.
ProgressAbrt is, by default, reraised so that code outside the context
manager can handle it. Therefore, we normally wrap the context block in a
try-except:
try:
with cn.progress('Something'):
# do something
except cn.ProgressAbrt:
# something went wrong
This reraising of the ProgressAbrt exception can be suppressed by using the
reraise argument which can be True or False. Setting this flag to
False silences the ProgressAbrt exception. At that point, we are still
able to do error handling using the onerror callback.
You can find a script in examples/progress.py which demonstrates a few
typical cases.
To quit the program, we call the quit() method on the Console object.
This method works the same way as sys.exit() (except that it takes one less
import to use it).
The default implementation of Console class automatically takes care of
SIGINT (keyboard interrupt) and SIGPIPE (broken pipe) signals. You can
customize the way those are handled by overloading the onint() and
onpipe() methods. You can also customize the registration of signals
themselves by overloading the register_signals() method.
Please report any bugs or feature requests to the issue tracker.