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A library that can print Python objects in human readable format


pip install objprint



Use op() (or objprint()) to print objects.

from objprint import op

class Position:
    def __init__(self, x, y):
        self.x = x
        self.y = y

class Player:
    def __init__(self): = "Alice"
        self.age = 18
        self.items = ["axe", "armor"]
        self.coins = {"gold": 1, "silver": 33, "bronze": 57}
        self.position = Position(3, 5)

<Player 0x7fe44e1e3070
  .age = 18,
  .coins = {'bronze': 57, 'gold': 1, 'silver': 33},
  .items = ['axe', 'armor'],
  .name = 'Alice',
  .position = <Position
    .x = 3,
    .y = 5

You can print multiple objects just like print, except op will print them in separate lines

op([1, 2], {'a': 1})
[1, 2]
{'a': 1}

op will return the same object it prints, so you can do something like this

a = MyObject()
# print the args inline with minumum change
# the difference is more significant with complex expressions
# original: function_using_object(a.f() + a.g())
function_using_object(op(a.f() + a.g()))

It works on multiple objects as well, as it returns a tuple, you need to unpack it for functions

a = MyObject()
function_using_object(*op(a.f(), a.g()))


If you want to use print() to print your object, you can also use the class decorator add_objprint to add __str__ method for your class.

from objprint import add_objprint

class Position:
    def __init__(self, x, y):
        self.x = x
        self.y = y

class Player:
    def __init__(self): = "Alice"
        self.age = 18
        self.items = ["axe", "armor"]
        self.coins = {"gold": 1, "silver": 33, "bronze": 57}
        self.position = Position(3, 5)

# This will print the same thing as above


If you want the str representation of the object, instead of printing it on the screen, you can use objstr function

from objprint import objstr

s = objstr(my_object)

print more

There are some optional information you can print with config.

"Public" Methods

There are no REAL public methods in python, here I simply meant you can print methods that do not start with __ as there will be a lot of default magic methods and you don't want that.

class Player:
    def attack(self, opponent):

op(Player(), print_methods=True)
<Player 0x7fe44e1e3070
  def attack(opponent)

As you can see, it will also print the method signature(without self argument).

Line numbers

You can print execution info, including the function it's in, the file and the line number of the printing line. This is helpful for you to locate where this object is printed.

def f():
    op(Player(), line_number=True)
f (
<Player 0x7f30e8cb1ac0

Argument names

You can print the expression of the argument with arg_name

op(Player(), arg_name=True)
<Player 0x7f495850a8d0


objprint supports print objects to json to make it easier to serialize an object.

objjson returns a jsonifiable object that can be dumped with json.dumps

from objprint import objjson

json_obj = objjson(Player())

print(json.dumps(json_obj, indent=2))
  ".type": "Player",
  "name": "Alice",
  "age": 18,
  "items": [
  "coins": {
    "gold": 1,
    "silver": 33,
    "bronze": 57
  "position": {
    ".type": "Position",
    "x": 3,
    "y": 5

You can use op to print in json format directly with format="json". You can pass in argument for json.dumps

op(Player(), format="json", indent=2)

add_objprint also works with format="json"

@add_objprint(format="json", indent=2)
class Player:

Enable/Disable the print

You can disable prints from all the op() calls globally with enable config.

from objprint import op

op([1, 2, 3])  # This won't print anything
op.enable()  # This could fix it!

Or you can use it for op() functions individually with some conditions

op(obj, enable=check_do_print())

attribute selection

You can customize which attribute to print with name filters.

objprint will try to match the attribute name with attr_pattern regex. The default attr_pattern is r"(!_).*", which means anything that does NOT start with an _.

You can customize attr_pattern to select the attributes you want to print:

# This will print all the attributes that do not start with __
op(Player(), attr_pattern=r"(!__).*")

You can also use include and exclude to specify attributes to print with regular expression so objprint will only print out the attributes you are interested in.

op(Player(), include=["name"])
  .name = 'Alice'
op(Player(), exclude=[".*s"])
<Player 0x7fe44e1e3070
  .name = 'Alice',
  .age = 18,
  .position = <Position
    .x = 3,
    .y = 5

If you specify both include and exclude, it will do a inclusive check first, then filter out the attributes that match exclusive check.

attr_pattern, include and exclude arguments work on objprint, objstr and @add_objprint.

Register Custom Type Formatter

You can also customize how certain types of objects are displayed by registering a custom formatter function to transform an object of a specific type into a string.

For example, you can print all integers in hexadecimal format by registering the hex() function for the int data type, or registering a custom lambda function.

from objprint import op

op.register_formatter(int, hex)
op.register_formatter(float, lambda x: f"{round(x, 3)}")
op(10)  # prints 0xa
op(3.14159)  # prints 3.142

Alternatively, you can also register a custom formatter function using a decorator:

def custom_formatter(obj: str):
    return f"custom_print: {obj}"

op("hi")  # prints custom_print: hi

During registration, objprint will examine the specified object type, and raise a TypeError if an invalid object type is provided.

When you finish using the custom formatters, you can unregister them with unregister_formatter().

op.unregister_formatter(int, float, str)
op(10)  # prints 10
op(3.14159)  # prints 3.14159
op("hi")  # prints hi

Or you can unregister everything by passing no argument to it.


The register_formatter() function also accepts an inherit argument (default True) to dictate if the registered formatter should also apply to any derived classes of the object type.

class BaseClass:
    name = 'A'

class DerivedClass(BaseClass):
    name = 'B'

With inherit=True, derived class will share the same formatter registered under base class.

def base_formatter(obj: BaseClass) -> str:
    return f'Print {} with Base Class Formatter'

op.register_formatter(BaseClass, base_formatter, inherit=True)

Print B with Base Class Formatter

With inherit=False, derived class will use the default formatter provided by objprint.

@op.register_formatter(BaseClass, inherit=False)
def base_formatter(obj: BaseClass) -> str:
    return f'Print {} with Base Class Formatter'

<DerivedClass 0x7fb42e8216a0
  .name = 'B'

If a derived class inherits from multiple base classes, each with a registered formatter, the chosen formatter adheres to the Method Resolution Order (MRO) of the derived class.

To check all the registered functions and their inheritance status, you can use the get_formatter() method. It returns a dictionary-like object that you can print for easy inspection.

fmts = op.get_formatter()
{<class '__main__.BaseClass'>: FormatterInfo(formatter=<function base_formatter at 0x7feaf33d1f70>, inherit=False)}

Please note that registering a formatter function with op will affect the output of objprint and objstr methods in the same way.


objprint formats the output based on some configs

  • config_name(default_value) - this config's explanation
  • enable(True) - whether to print, it's like a switch
  • depth(100) - how deep objprint goes into nested data structures
  • indent(2) - the indentation
  • width(80) - the maximum width a data structure will be presented as a single line
  • elements(-1) - the maximum number of elements that will be displayed, -1 means no restriction
  • color(True) - whether to use colored scheme
  • line_number(False) - whether to print the function (filename:line_number) before printing the object
  • arg_name(False) - whether to print the argument expression before the argument value
  • skip_recursion(True) - whether skip printing recursive data, which would cause infinite recursion without depth constraint
  • honor_existing(True) - whether to use the existing user defined __repr__ or __str__ method
  • attr_pattern(r"(!_).*") - the regex pattern for attribute selection
  • include([]) - the list of attribute regex to do an inclusive filter
  • exclude([]) - the list of attribute regex to do an exclusive filter

You can set the configs globally using config function

from objprint import config

Or if you don't want to mess up your name space

from objprint import op

Or you can do a one time config by passing the arguments into objprint function

from objprint import op

op(var, indent=4)


Maybe you don't want to import op in every single file that you want to use. You can use install to make it globally accessible

from objprint import op, install

# Now you can use op() in any file

# This is the same

# You can specify a name for objprint()


Please send bug reports and feature requests through github issue tracker.


Copyright Tian Gao, 2020-2021.

Distributed under the terms of the Apache 2.0 license.


A library that can print Python objects in human readable format







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