pipepy

A Python library for invoking and interacting with shell commands

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Project description

A Python library for invoking and interacting with shell commands.

Build

Why? Comparison with other similar frameworks
Installation and testing
Intro, basic usage
Laziness
Customizing commands
Redirecting output to files
Pipes
Running in the background
Binary mode
Streaming to console
Utils
"Interactive" mode
pymake
TODOs

Why? Comparison with other similar frameworks

Xonsh: Xonsh allows you to combine shell and Python and enables very powerful scripting and interactive sessions. This library does the same to a limited degree. However, Xonsh introduces a new language that is a superset of Python. The main goal of this library that sets it apart is that it is intended to be a pure Python implementation, mainly aimed at scripting.
sh and pieshell: These are much closer to the current library in that they are pure Python implementations. The current library, however, tries to improve on the following aspects:
- It tries to apply more syntactic sugar to make the invocations feel more like shell invocations.
- It tries to offer ways to have shell commands interact with python code in powerful and intuitive ways.

Installation and testing

python -m pip install pipepy

Or, if you want to modify the code while trying it out:

git clone https://github.com/kbairak/pipepy
cd pipepy
python -m pip install  -e .

To run the tests, you need to first install the testing requirements:

python -m pip install -r test_requirements.txt

pymake test
# or
pytest

There are a few more pymake targets to assist with testing during development:

covtest: Produces and opens a coverage report
watchtest: Listens for changes in the source code files and reruns the tests automatically
debugtest: Runs the tests without capturing their output so that you can insert a debug statement

pymake is a console script that is part of pipepy that aims to be a replacement for GNU make, with the difference that the Makefiles are written in Python. More on this below.

Intro, basic usage

from pipepy import ls, grep

print(ls)  # prints contents of current folder
if ls | grep('info.txt'):
      print('info.txt found')

Most shell commands are importable straight from the pipepy module. Dashes in commands' names are converted to underscore (docker-compose → docker_compose). Commands that cannot be found automatically can be created with the PipePy constructor:

from pipepy import PipePy

custom_command = PipePy('./bin/custom')
python_script = PipePy('python', 'script.py')

Laziness

Commands are evaluated lazily. For example, this will not actually do anything:

from pipepy import wget
wget('http://...')

A command will be evaluated when its output is used. This can be done with the following ways:

Accessing the returncode, stdout and stderr properties

Evaluating the command as a boolean object:

from pipepy import ls, grep
if ls | grep('info.txt'):
    print("info.txt found")

The command will be truthy if its returncode is 0.

Evaluating the command as a string object
```
from pipepy import ls
result = str(ls)
# or
print(ls)
```
Converting a command to a str returns its stdout.

Invoking the .as_table() method:

from pipepy import ps
ps.as_table()
# <<< [{'PID': '11233', 'TTY': 'pts/4', 'TIME': '00:00:01', 'CMD': 'zsh'},
# ...  {'PID': '17673', 'TTY': 'pts/4', 'TIME': '00:00:08', 'CMD': 'ptipython'},
# ...  {'PID': '18281', 'TTY': 'pts/4', 'TIME': '00:00:00', 'CMD': 'ps'}]

Iterating over a command object:

This iterates over the lines of the command's stdout:

from pipepy import ls
for filename in ls:
    print(filename.upper)

command.iter_words() iterates over the words of the command's stdout:

from pipepy import ps
list(ps.iter_words())
# <<< ['PID', 'TTY', 'TIME', 'CMD',
# ...  '11439', 'pts/5', '00:00:00', 'zsh',
# ...  '15532', 'pts/5', '00:00:10', 'ptipython',
# ...  '15539', 'pts/5', '00:00:00', 'ps']

Redirecting the output to something else (this will be further explained below):

from pipepy import ls, grep
ls > 'files.txt'
ls >> 'files.txt'
ls | grep('info.txt')  # `ls` will be evaluated, `grep` will not
ls | lambda output: output.upper()

Redirecting from an iterable (this will be further explained below):

from pipepy import grep
(f"{i}\n" for i in range(5)) | grep(2)

If you are not interested in the output of a command but want to evaluate it nevertheless, you can call it with empty arguments. So, this will actually invoke the command (and wait for it to finish).

from pipepy import wget
wget('http://...')()

Customizing commands

Calling a command with non empty arguments will return a modified unevaluated copy. So the following are equivalent:

from pipepy import PipePy
ls_l = PipePy('ls', '-l')
# Is equivalent to
ls_l = PipePy('ls')('-l')

There is a number of other ways you can customize a command:

Globs: globbing will be applied to all positional arguments:

from pipepy import echo
print(echo('*'))  # Will print all files in the current folder

You can use glob.escape if you want to avoid this functionality:

import glob
from pipepy import ls, echo

print(ls)
# <<< **a *a *aa

print(echo('*a'))
# <<< **a *a *aa

print(echo(glob.escape('*a')))
# <<< *a

Keyword arguments:

from pipepy import ls
ls(sort="size")     # Equivalent to ls('--sort=size')
ls(sort_by="size")  # Equivalent to ls('--sort-by=size')
ls(escape=True)     # Equivalent to ls('--escape')
ls(escape=False)    # Equivalent to ls('--no-escape')

Since keyword arguments come after positional arguments, if you want the final command to have a different ordering you can invoke the command multiple times:

from pipepy import ls
ls('-l', sort="size")  # Equivalent to ls('-l', '--sort=size')
ls(sort="size")('-l')  # Equivalent to ls('--sort=size', '-l')

Attribute access:

from pipepy import git
git.push.origin.bugfixes  # Equivalent to git('push', 'origin', 'bugfixes')

Minus sign:

from pipepy import ls
ls - 'l'        # Equivalent to ls('-l')
ls - 'default'  # Equivalent to ls('--default')

This is to enable making the invocations look more like the shell:

from pipepy import ls
l, t = 'l', 't'
ls -l -t  # Equivalent to ls('-l', '-t')

You can call pipepy.overload_chars(locals()) in your script to assign all ascii letters to variables of the same name.

from pipepy import ls, overload_chars
overload_chars(locals())
ls -l -t  # Equivalent to ls('-l', '-t')

Redirecting output to files

The >, >> and < operators work similar to how they work in a shell:

ls               >  'files.txt'  # Will overwrite files.txt
ls               >> 'files.txt'  # Will append to files.txt
grep('info.txt') <  'files.txt'  # Will use files.txt as input

Pipes

The | operator is used to customize where a command gets its input from and what it does with its output. Depending on the types of the operands, different behaviors will emerge:

1. Both operands are commands

If both operands are commands, the result will be as similar as possible to what would have happened in a shell:

from pipepy import git, grep
if git.diff(name_only=True) | grep('readme.txt'):
      print("readme was changed")

If the left operand was previously evaluated, then it's output (stdout) will be passed directly as inputs to the right operand. Otherwise, both commands will be executed in parallel and left's output will be streamed into right.

2. Left operand is a string

If the left operand is a string, it will be used as the command's stdin:

from pipepy import grep
result = "John is 18 years old\nMary is 25 years old" | grep("Mary")
print(result)
# <<< Mary is 25 years old

3. Left operand is any kind of iterable

If the left operand is any kind of iterable, its elements will be fed to the command's stdin one by one:

import random
from pipepy import grep

result = ["John is 18 years old\n", "Mary is 25 years old"] | grep("Mary")
print(result)
# <<< Mary is 25 years old

def my_stdin():
      for _ in range(500):
            yield f"{random.randint(1, 100)}\n"

result = my_stdin() | grep(17)
print(result)
# <<< 17
# ... 17
# ... 17
# ... 17
# ... 17

4. Right operand is a function

The function's arguments need to either be:

a subset of returncode, output, errors or
a subset of stdout, stderr

The ordering of the arguments is irrelevant since the function's signature will be inspected to assign the proper values.

In the first case, the command will be waited for and its evaluated output will be made available to the function's arguments.

from pipepy import wc

def lines(output):
    for line in output.splitlines():
        try:
            lines, words, chars, filename = line.split()
        except ValueError:
            continue
        print(f"File {filename} has {lines} lines, {words} words and {chars} "
              "characters")

wc('*') | lines
# <<< File demo.py has 6 lines, 15 words and 159 characters
# ... File main.py has 174 lines, 532 words and 4761 characters
# ... File interactive2.py has 10 lines, 28 words and 275 characters
# ... File interactive.py has 12 lines, 34 words and 293 characters
# ... File total has 202 lines, 609 words and 5488 characters

In the second case, the command will be executed in the background and its stdout and stderr streams will be made available to the function.

import re
from pipepy import ping

def mean_ping(stdout):
    pings = []
    lines = iter(stdout)
    while True:
        try:
            line = next(lines)
        except StopIteration:
            break
        match = re.search(r'time=([\d\.]+) ms$', line.strip())
        if not match:
            continue
        time = float(match.groups()[0])
        pings.append(time)
        if len(pings) % 10 == 0:
            print(f"Mean time is {sum(pings) / len(pings)} ms")

ping('-c', 30, "google.com") | mean_ping
# >>> Mean time is 71.96000000000001 ms
# ... Mean time is 72.285 ms
# ... Mean time is 72.19666666666667 ms

Running in the background

You can run commands in the background by calling the _d (mnemonic: daemon) attribute. At a later point you can wait for them to finish with .wait().

import time
from pipepy import sleep

def main():
   start = time.time()

   print(f"Starting background process at {time.time() - start}")
   result = sleep(3)._d()

   print(f"Printing message at {time.time() - start}")

   print(f"Waiting for 1 second in python at {time.time() - start}")
   time.sleep(1)

   print(f"Printing message at {time.time() - start}")

   print(f"Waiting for process to finish at {time.time() - start}")
   result.wait()

   print(f"Process finished at {time.time() - start}")

main()
# <<< Starting background process    at 0.0000004768371582031
# ... Printing message               at 0.0027723312377929688
# ... Waiting for 1 second in python at 0.0027921199798583984
# ... Printing message               at 1.0040225982666016
# ... Waiting for process to finish  at 1.0040972232818604
# ... Process finished               at 3.004188776016235

Interracting with background processes

There are 3 ways to interact with a background process: read-only, write-only and read/write. We have already covered read-only and write-only:

1. Incrementally sending data to a command

This is done by piping from an iterable to a command. The command actually runs in the background and the iterable's data is fed to it as it becomes available. We will slightly modify the previous example to better demonstrate this:

import random
import time
from pipepy import grep

def my_stdin():
    start = time.time()
    for _ in range(500):
        time.sleep(.01)
        yield f"{time.time() - start} {random.randint(1, 100)}\n"

my_stdin() | grep('-E', r'\b17$', _stream_stdout=True)
# <<< 0.3154888153076172 17
# ... 1.5810892581939697 17
# ... 1.7773401737213135 17
# ... 2.8303775787353516 17
# ... 3.4419643878936768 17
# ... 4.511774301528931  17

Here, grep is actually run in the background and matches are printed as they are found since the command's output is being streamed to the console, courtesy of the _stream_stdout argument (more on this below).

2. Incrementally reading data from a command

This can be done by iterating over a command's output:

import time
from pipepy import ping

start = time.time()
for line in ping('-c', 3, 'google.com'):
    print(time.time() - start, line.strip().upper())
# <<< 0.15728354454040527 PING GOOGLE.COM (172.217.169.142) 56(84) BYTES OF DATA.
# ... 0.1574106216430664  64 BYTES FROM SOF02S32-IN-F14.1E100.NET (172.217.169.142): ICMP_SEQ=1 TTL=103 TIME=71.8 MS
# ... 1.1319730281829834  64 BYTES FROM 142.169.217.172.IN-ADDR.ARPA (172.217.169.142): ICMP_SEQ=2 TTL=103 TIME=75.3 MS
# ... 2.1297826766967773  64 BYTES FROM 142.169.217.172.IN-ADDR.ARPA (172.217.169.142): ICMP_SEQ=3 TTL=103 TIME=73.4 MS
# ... 2.129857063293457
# ... 2.129875659942627   --- GOOGLE.COM PING STATISTICS ---
# ... 2.1298911571502686  3 PACKETS TRANSMITTED, 3 RECEIVED, 0% PACKET LOSS, TIME 2004MS
# ... 2.129910707473755   RTT MIN/AVG/MAX/MDEV = 71.827/73.507/75.253/1.399 MS

Again, the ping command is actually run in the background and each line is given to the body of the for-loop as it becomes available.

Another way is to pipe the command to a function that has a subset of stdin and stdout as its arguments, as we demonstrated before.

3. Reading data from and writing data to a command

Lets assume we have a command that makes the user take a math quiz. A normal interaction with this command would look like this:

→ math_quiz
3 + 4 ?
→ 7
Correct!
8 + 2 ?
→ 12
Wrong!
→ Ctrl-d

Using python to interact with this command in a read/write fashion can be done with a with statement:

from pipepy import math_quiz

result = []
with math_quiz as (stdin, stdout, stderr):
    stdout = (line.strip() for line in stdout if line.strip())
    try:
        for _ in range(3)
            question = next(stdout)
            a, _, b, _ = question.split()
            answer = str(int(a) + int(b))
            stdin.write(answer + "\n")
            stdin.flush()
            verdict = next(stdout)
            result.append((question, answer, verdict))
    except StopIteration:
        pass

result
# <<< [('10 + 7 ?', '17', 'Correct!'),
# ...  ('5 + 5 ?', '10', 'Correct!'),
# ...  ('5 + 5 ?', '10', 'Correct!')]

stdin, stdout and stderr are the open file streams of the background process. When the body of the with block finishes, an EOF is sent to the process and it is waited for.

You need to remember to end lines fed to stdin with a newline character if the command expects it. Also, don't forget to call stdin.flush() every now and then.

If you want to capture the returncode of the command after the with block finishes, you must call it on a background command, which will have been waited for when the block ends:

from pipepy import math_quiz

job = math_quiz._d()

with job as (stdin, stdout, stderr):
    ...

if job:  # No need to `job.wait()`
    print("Math quiz successful")
else:
    print("Math quiz failed")

Binary mode

All commands are executed in text mode, which means that they deal with str objects. This can cause problems. For example:

from pipepy import gzip
result = "hello world" | gzip
print(result.stdout)
# <<< Traceback (most recent call last):
# ... ...
# ... UnicodeDecodeError: 'utf-8' codec can't decode byte 0x8b in position 1: invalid start byte

gzip cannot work in text mode because its output is binary data that cannot be utf-8-decoded. When text mode is not desirable, a command can be converted to binary mode by accessing the _b (mnemonic: binary) attribute:

from pipepy import gzip
result = "hello world" | gzip._b
print(result.stdout)
# <<< b'\x1f\x8b\x08\x00\x00\x00\x00\x00\x00\x03\xcbH\xcd\xc9\xc9W(\xcf/\xcaI\xe1\x02\x00-;\x08\xaf\x0c\x00\x00\x00'

Input and output will be converted from/to binary by using the 'UTF-8' encoding. In the previous example, our input's type was str and was utf-8-encoded before being fed into gzip. You can change the encoding with the _encoding keyword argument:

from pipepy import gzip
result = "καλημέρα" | gzip._b
print(result.stdout)
# <<< b'\x1f\x8b\x08\x00\x00\x00\x00\x00\x00\x03\x01\x10\x00\xef\xff\xce\xba\xce\xb1\xce\xbb\xce\xb7\xce\xbc\xce\xad\xcf\x81\xce\xb1"\x15g\xab\x10\x00\x00\x00'
result = "καλημέρα" | gzip._b(_encoding="iso-8859-7")
print(result.stdout)
# <<< b'\x1f\x8b\x08\x00\x00\x00\x00\x00\x00\x03{\xf5\xf0\xf5\xf37w?>\x04\x00\x1c\xe1\xc0\xf7\x08\x00\x00\x00'

Streaming to console

During invocation, you can set the _stream_stdout and _stream_stderr keyword arguments to True. This means that the respective stream will not be captured by the result, but streamed to the console. This allows the user to interact with interactive commands. Consider the following 2 examples:

fzf works like this:
1. It gathers a list of choices from its stdin
2. It displays the choices on stderr, constantly refreshing it depending on what the user inputs
3. It starts directly capturing keystrokes on the keyboard, bypassing stdin, to allow the user to make their choice.
4. When the user presses Enter, it prints the choice to its stdout
Taking all this into account, we can do the following:
```
from pipepy import fzf
fzf = fzf(_stream_stderr=True)

# This will open an fzf session to let us choose between "John" and "Mary"
print("John\nMary" | fzf)
# <<< Mary
```

dialog works similar to fzf, but swaps stdout with stderr:

It gathers a list of choices from its arguments
It displays the choices on stdout, constantly refreshing it depending on what the user inputs
It starts directly capturing keystrokes on the keyboard, bypassing stdin, to allow the user to make their choice.
When the user presses Enter, it prints the choice to its stderr

Taking all this into account, we can do the following:

from pipepy import dialog
dialog = dialog(_stream_stdout=True)

# This will open a dialog session to let us choose between "John" and "Mary"
result = dialog(checklist=True)('Choose name', 30, 110, 0,
                                "John", '', "on",
                                "Mary", '', "off")
print(result.stderr)
# <<< John

Also, during a script, you may not be interested in capturing the output of a command but may want to stream it to the console to show the command's output to the user. A shortcut for setting both _stream_stdout and _stream_stderr to True is the _s (mnemonic: stream) attribute:

from pipepy import wget

wget('https://...')._s()

While stdout and stderr will not be captured, returncode will and thus you can still use the command in boolean expressions:

from pipepy import wget

if wget('https://...')._s:
     print("Download succeeded")
else:
     print("Download failed")

You can call pipepy.set_always_stream(True) to make streaming to the console the default behavior. This may be desirable in some situations, like Makefiles (see below).

from pipepy import set_always_stream, ls
set_always_stream(True)
ls()  # Alsost equivalent to `ls._s()`
set_always_stream(False)

Similarly to how ._s forces a command to stream its output to the console, ._c (mnemonic capture) forces it to capture its output even if set_always_stream has been called:

from pipepy import set_always_stream, ls
set_always_stream(True)
ls()     # Will stream its output
ls._c()  # Will capture its output
set_always_stream(False)

Exceptions

You can call .raise_for_returncode() on an evaluated result to raise an exception if its returncode is not 0 (think of requests's .raise_for_status()):

from pipepy import ping, PipePyError
result = ping("asdf")()  # Remember, we have to evaluate it first

result.raise_for_returncode()
# <<< PipePyError: (2, '', 'ping: asdf: Name or service not known\n')

try:
    result.raise_for_returncode()
except PipePyError as exc:
    print(exc.returncode)
    # <<< 2
    print(exc.stdout)
    # <<< ""
    print(exc.stderr)
    # <<< ping: asdf: Name or service not known

You can call ._r (mnemonic raise) on a command to have it always raise an exception upon evaluation if its returncode ends up not being zero:

from pipepy import ping
ping("asdf")._r()
# <<< PipePyError: (2, '', 'ping: asdf: Name or service not known\n')

You can call pipepy.set_always_raise(True) to have all commands raise an exception if their returncode is not zero.

from pipepy import ping, set_always_raise
set_always_raise(True)
ping("asdf")()
# <<< PipePyError: (2, '', 'ping: asdf: Name or service not known\n')

If "always raise" is set, you can modify a command to not raise an exception by calling ._q (mnemonic quiet) on it.

from pipepy import ping, set_always_raise
set_always_raise(True)
try:
    ping("asdf")()  # Will raise an exception
except Exception as exc:
    print(exc)
# <<< PipePyError: (2, '', 'ping: asdf: Name or service not known\n')

try:
    ping("asdf")._q()  # Will not raise an exception
except Exception as exc:
    print(exc)

Utils

Since changing the current working directory or the environment in a subprocess has no effect on the current process, we include the pipepy.cd and pipepy.export functions. These are not PipePy instances but simple aliases to os.chdir and os.environ.__setitem__ respectively.

"Interactive" mode

When "interactive" mode is set, the __repr__ method will simply return self.stdout + self.stderr. This enables some very basic functionality for the interactive python shell. To set interactive mode, run pipepy.set_interactive(True):

from pipepy import ls, set_interactive, overload_chars
set_interactive(True)
ls
# <<< demo.py
# ... interactive2.py
# ... interactive.py
# ... main.py

overload_chars(locals())
ls -l
# <<< total 20
# ... -rw-r--r-- 1 kbairak kbairak  159 Feb  7 22:05 demo.py
# ... -rw-r--r-- 1 kbairak kbairak  275 Feb  7 22:04 interactive2.py
# ... -rw-r--r-- 1 kbairak kbairak  293 Feb  7 22:04 interactive.py
# ... -rw-r--r-- 1 kbairak kbairak 4761 Feb  8 20:42 main.py

`pymake`

Bundled with this library there is a command called pymake which aims to replicate the syntax and behavior of GNU make as much as possible, but in Python. A Makefile.py file looks like this (this is actually part of the Makefile of the current library):

from pipepy import python, rm


def clean():
    rm('-rf', "build", "dist")._s()

def build(clean):
    python('-m', "build")._s()

def publish(build):
    python('-m', "twine").upload("dist/*")._s()

You can now run pymake publish to run the publish make target, along with its dependencies. The names of the arguments of the functions are used to define the dependencies, so clean is a dependency of build and build is a dependency of publish. As you can see, the pipepy library is a very good fit for pymake's Makefiles.

The arguments hold any return values of the dependency targets:

def a():
    return 1

def b():
    return 2

def c(a, b):
    print(a + b)

pymake c will print 3.

Each dependency will be executed at most once, even if it's used as a dependency more than once:

def a():
    print("pymake target a")

def b(a):
    print("pymake target b")

def c(a, b):
    print("pymake target c")

→ pymake c
pymake target a
pymake target b
pymake target c

You can set the DEFAULT_PYMAKE_TARGET global variable to define the default target.

from pipepy import pytest

DEFAULT_PYMAKE_TARGET = "test"

def test():
    pytest._s()

TODOs

Ability to source bash files
Pass arguments to pymake (see what other tricks make does for inspiration)
Context processors for cd and/or environment
Add more docstrings
Stream and capture stdout and stderr at the same time
Python virtual environments (maybe sourcing bash files will suffice)

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pipepy 0.0.6

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Intro, basic usage

Laziness

Customizing commands

Redirecting output to files

Pipes

1. Both operands are commands

2. Left operand is a string

3. Left operand is any kind of iterable

4. Right operand is a function

Running in the background

1. Incrementally sending data to a command

2. Incrementally reading data from a command

3. Reading data from and writing data to a command

Binary mode

Streaming to console

Exceptions

Utils

"Interactive" mode

pymake

TODOs

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`pymake`