Do you ever use print() or log() to debug your code? Of course you do. IceCream, or ic for short, makes print debugging a little sweeter.

IceCream is well tested, permissively licensed, and supports Python 2, Python 3, PyPy2, and PyPy3.

Have you ever printed variables or expressions to debug your program? If you've ever typed something like

print(foo('123'))

or the more thorough

print("foo('123')", foo('123'))

then ic() is here to help. With arguments, ic() inspects itself and prints both its own arguments and those argument's values.

from icecream import ic

def foo(i):
    return i + 333

ic(foo(123))

Prints

ic| foo(123): 456

Similarly,

d = {'key': {1: 'one'}}
ic(d['key'][1])

class klass():
    attr = 'yep'
ic(klass.attr)

Prints

ic| d['key'][1]: 'one'
ic| klass.attr: 'yep'

Just give ic() a variable or expression and you're done. Easy.

Have you ever used print() to determine which parts of your program are executed, and in which order they're executed? For example, if you've ever added print statements to debug code like

def foo():
    print(0)
    first()

    if expression:
        print(1)
        second()
    else:
        print(2)
        third()

then ic() helps here, too. Without arguments, ic() inspects itself and prints the calling filename and line number.

from icecream import ic

def foo():
    ic()
    first()
    
    if expression:
        ic()
        second()
    else:
        ic()
        third()

Prints

ic| example.py:4 in foo()
ic| example.py:11 in foo()

Just call ic() and you're done. Simple.

ic() returns its argument(s), so ic() can easily be added to, and debug, pre-existing code.

>>> a = 6
>>> def half(i):
>>>     return i / 2
>>> b = half(ic(a))
ic| a: 6
>>> ic(b)
ic| b: 3

ic.format(*args) can be used to generate and return ic() output as a string directly.

>>> from icecream import ic
>>> s = ic.format('sup')
>>> print(s)
ic| 'sup': 'sup'

Additionally, ic()'s output can be entirely disabled, and later re-enabled, with ic.disable() and ic.enable() respectively.

from icecream import ic

ic(1)

ic.disable()
ic(2)

ic.enable()
ic(3)

Prints

ic| 1: 1
ic| 3: 3

ic() continues to return its arguments when disabled, of course; no existing code with ic() breaks.

ic.configureOutput(prefix, outputFunction, argToStringFunction, includeContext) can be used to adopt a custom output prefix (the default is ic| ), change the output function (default is to write to stderr), customize how arguments are serialized to strings, and/or include the ic() call's context (filename, line number, and parent function) in ic()'s output.

>>> from icecream import ic
>>> ic.configureOutput(prefix='hello -> ')
>>> ic('world')
hello -> 'world': 'world'

prefix can optionally be a function, too.

>>> import time
>>> from icecream import ic
>>>  
>>> def unixTimestamp():
>>>     return '%i |> ' % int(time.time())
>>>
>>> ic.configureOutput(prefix=unixTimestamp)
>>> ic('world')
1519185860 |> 'world': 'world'

outputFunction, if provided, is called with ic()'s output instead of that output being written to stderr (the default).

>>> import logging
>>> from icecream import ic
>>>
>>> def warn(s):
>>>     logging.warning(s)
>>>
>>> ic.configureOutput(outputFunction=warn)
>>> ic('eep')
WARNING:root:ic| 'eep': 'eep'

argToStringFunction, if provided, is called with argument values to be serialized to printable strings. The default is PrettyPrinter's pprint.pformat, but this can be changed to, for example, handle non-standard datatypes in a custom fashion.

>>> from icecream import ic
>>> 
>>> def toString(obj):
>>>    if isinstance(obj, str):
>>>        return '[!string %r with length %i!]' % (obj, len(obj))
>>>    return repr(obj)
>>> 
>>> ic.configureOutput(argToStringFunction=toString)
>>> ic(7, 'hello')
ic| 7: 7, 'hello': [!string 'hello' with length 5!]

includeContext, if provided and True, adds the ic() call's filename, line number, and parent function to ic()'s output. includeContext is False by default.

>>> from icecream import ic
>>> ic.configureOutput(includeContext=True)
>>> 
>>> def foo():
>>>   ic('str')
>>> foo()

Prints

ic| example.py:12 in foo()- 'str': 'str'

Installing IceCream with pip is easy.

$ pip install icecream

IceCream should be enjoyed with every language.

• JavaScript: node-icecream

If you'd like a similar ic() function in your favorite language, please open a pull request! IceCream's goal is to sweeten print debugging with a handy-dandy ic() function in every language.