Get Last Result in Interactive Python Shell

Get last result in interactive Python shell

Underscore.

>>> 5+5
10
>>> _
10
>>> _ + 5
15
>>> _
15

Why does _ not always give me the last result in interactive shell

The reason is pretty simple- try doing

[i for i in range(1000)]

and then accessing i- you'll see that i isn't defined (it's scope is within the list comprehension- when you exit the list comprehension, there "is no i").

This is in contrast to a for loop, where the scope of i is NOT within the actual for loop- so you can access it from outside.

So if we go to your case (with the _), if the _ is defined, like with a regular for loop, then you need to del it. If you do it within a list comprehension, once the list comprehension is over, the underscore is no longer defined- which means it'll just be the last value

How to repeat last command in python interpreter shell?

I use the following to enable history on python shell.

This is my .pythonstartup file . PYTHONSTARTUP environment variable is set to this file path.

# python startup file 
import readline 
import rlcompleter 
import atexit 
import os 
# tab completion 
readline.parse_and_bind('tab: complete') 
# history file 
histfile = os.path.join(os.environ['HOME'], '.pythonhistory') 
try: 
    readline.read_history_file(histfile) 
except IOError: 
    pass 
atexit.register(readline.write_history_file, histfile) 
del os, histfile, readline, rlcompleter

You will need to have the modules readline, rlcompleter to enable this.

Check out the info on this at : http://docs.python.org/using/cmdline.html#envvar-PYTHONSTARTUP.

Modules required:

1. http://docs.python.org/library/readline.html
2. http://docs.python.org/library/rlcompleter.html

How to get the python interactive shell output of a python code in a variable?

if you really must run strings as python code, you COULD spawn another python process with the subprocess.Popen function, specify stdout, stderr, stdin each to subprocess.PIPE and use the .communicate() function to retrieve the output.

python takes a -c argument to specify you're giving it python code as the next argument to execute/interpret.

IE python -c "print(5+5)" will output 10 to stdout

IE

proc = subprocess.Popen(["python", "-c", code], stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
stdout, stderr = proc.communicate()
print(stdout.decode('utf-8'))

Is there any python equivalent of haskell's it , to get last successful command in REPL

_ will give you the result of the last line evaluated (that wasn't None).

Python 3.7.1 (default, Nov  8 2018, 09:08:57)
[Clang 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 2+5
7
>>> _
7

How do I retrieve the output of a previous command and save it in a variable inside the Python interactive shell?

_ (single underscore) works for me in python 3 for windows, should work for other versions as well:

>>> 1 + 1
2
>>> x = _
>>> x
2

Get result of line above

This behavior of _ is only available in REPL. _ holds the output of that the last expression evaluated to. It should be noted, if the previous expression produced a TRACEBACK, _ will hold the last valid output. You could also chain _ upto three times (in IPython), to go fetch the 3rd last output:

>>> 5
5
>>> 6
6
>>> 7
7
>>> ___
5
>>> __
7
>>> _
7

If you use it in actual scripts, you can treat it _ as a variable name (not recommended, if you plan to use the variable), for example:

_ = 10
print(_)

# will print 10

But the behavior you get at REPL can't be emulated in an actual script.

---

Related Topics