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Intuitive inspect and expect

Project description

Intuitive inspect and expect

Table of Contents


Simply install it from pypi:

pip install inxpect

or from sources:

git clone
cd inxpect
python install


  • Build properties inspector from a type or object
  • Can inspect objects recursively (default depth is 0)
  • Defines a set of chainable expectations within properties types
  • Provides a set of operators
  • Each operator support is_true and is_false methods
  • Can inject getters to operators and expectations constructors
  • Can inject getter closures to expectations
  • Getters, operators and expectations are serializables and searchables
  • Expectations results are tunables (returns booleans, raises exceptions, log…)
  • tested with python versions 2.7, 3.2 and 3.3

Chainable expectations


  • equal_to, not_equal_to, same_as, not_same_as
  • lower_than, lower_or_equal_than, greater_than, greater_or_equal_than
  • type_is, type_is_not, instance_of, not_instance_of
  • len, and, or
  • operators symbols: ==, !=, >, >=, <, <=, ‘|’ (for or), ‘&’ (for and)

Lists and Tuples:

  • has, has_all, has_any
  • has_key, has_keys, has_any_key
  • at


  • has_item, has_items, has_any_item
  • has_key, has_keys, has_any_key
  • has_value, has_values, has_any_value
  • at


  • Equal, NotEqual, SameAs, NotSameAs
  • LowerThan, LowerOrEqualThan, GreaterThan, GreaterOrEqualThan
  • TypeIs, TypeIsNot, InstanceOf, NotInstanceOf
  • Contains, NotContains, ContainsAny, ContainsAll
  • ContainsItem, ContainsAllItem, ContainsAnyItem
  • ContainsValue, ContainsAllValue, ContainsAnyValue

Quick example

from inxpect.expect.operator import Equal
from inxpect import And, Or

equal_2 = Equal(2)
assert  equal_2(2)
assert equal_2(3) is False

assert Equal.is_true(2, 2)
assert Equal.is_false(2, 3)

# You can use a getter function:
mod_3 = lambda num: num % 3
multiple_of_3 = Equal(0, mod_3)

assert multiple_of_3(15)
assert multiple_of_3(16) is False

# chaining:
mod_5 = lambda num: num % 5
multiple_of_5 = Equal(0, mod_5)

multiple_of_3_and_5 = And(multiple_of_3, multiple_of_5)
multiple_of_3_or_5 = Or(multiple_of_3, multiple_of_5)

assert multiple_of_3_and_5(15)
assert multiple_of_3_or_5(16) is False

multiple_of_4 = Equal(0, lambda num: num % 4)

multiple_of_3_4_or_5 = multiple_of_3_or_5 | multiple_of_4

assert multiple_of_3_4_or_5(16)

# As multiple_of_3_or_5 is Or chain multiple_of_4 is just appended
assert multiple_of_3_4_or_5 is multiple_of_3_or_5

# With And a new And chain is returned:
assert (multiple_of_3_or_5 is multiple_of_3_or_5 & multiple_of_4) is False

# Testing and search (lambda is partially pickled):
assert (multiple_of_5 == Equal(0, lambda num: num % 5))
# Comparison is made on bytecode
assert (multiple_of_5 == Equal(0, lambda num: num % 4)) is False
# Comparison is made on arguments (and their name)
assert (multiple_of_5 == Equal(0, lambda num, *args: num % 5)) is False



Each example uses these 2 weird classes:

class Subject(object):
  args = tuple()
  kwargs = dict()
  def __call__(self, event):
    self.args = event.args
    self.kwargs = event.kwargs
    event.result = False

class EventData(object):
  name = 'event'
  subject = Subject()
  args = tuple()
  kwargs = dict()
  result = True

  def __init__(self, **kwargs):
    for attr, value in kwargs.items():
      setattr(self, attr, value)


Nothing hard, just a function “expect_factory” wich take an object or a type as template and returns an inspector wich contains properties named like ones of the given template. Inspector properties are operations which helps to make expectations on objects with same properties (name, and expected type) as template.

“expect_factory” takes an optional second argument (by default 0) to precise the depth of recursion. Each property containing an object will be replaced by an inspector until depth, otherwise, object become an “ExpectSame” object.

import inxpect

expect = inxpect.expect_factory(EventData)
assert hasattr(expect, 'result')
assert hasattr(expect.subject, 'args') is False
# with depth to 1:
expect = inxpect.expect_factory(EventData, 1)
assert hasattr(expect.subject, 'args')

Expect Basics

import inxpect

expect = inxpect.expect_factory(EventData)

name_is_event1 ='event1')  # can be done with ==
result_is_not_None = expect.result != None
is_event1 = name_is_event1 & result_is_not_None

event1 = EventData(name='event1')
event2 = EventData(name='event2', result=None)

assert result_is_not_None(event1)
assert result_is_not_None(event2) is False

assert name_is_event1(event1)
assert name_is_event1(event2) is False

log = []
expected = 'Name %s is not "event1"'

def is_event1_fails(chain, at, *args, **kwargs):
  # args and kwargs are same passed to is_event1:
  event = args[0]
  if at in'event1'):
    log.append(expected %
  return False


assert is_event1(event1)
assert is_event1(event2) is False

assert log[0] == expected % 'event2'

Expect Closures

As briefly seen, operators can take a getter argument. That’s what is done by inspect that use AttrByName getter to return an attribute by its name.

In addition to this, each assertion (equal_to…) can take a closure argument, wich is a function that take getter result as argument and return the value to test.

Internally, this mecanism is used to provide ‘at’ and ‘len’ assertions, the example above illustrate how ‘len’ functions.

import inxpect

expect = inxpect.expect_factory(EventData)

name_len_is_5 =, len)

event1 = EventData()
event2 = EventData(name='0123456789')

assert name_len_is_5(event1)
assert name_len_is_5(event2) is False

# the closure also encapsulate len for comparisons
assert name_len_is_5 ==, len)

### Details:
# Never use this but it shows how len is encapsulated

# func is the internal varname, needed to compare bytecode
func = len
# Lambda permit to get bytecode from __code__ attibute
func_len = lambda *args, **kwargs: func(*args, **kwargs)
not_func_len = lambda *args, **kwargs: len(*args, **kwargs)

assert (name_len_is_5 ==, func_len))
# assert it compares bytecode
assert (name_len_is_5 ==, not_func_len)) is False

Expect Should

In case default operators are not sufficient, you can define yours and use them easily with should. An operator is a simple class that extends Operator (located in inxpect.expect.operator) which need the class method “is_true(cls, given, expected)” to returns a boolean.

from inxpect.expect import Expect
from inxpect.expect.operator import Operator

class MultipleOf5(Operator):
    def is_true(cls, given, expected):
        return given % 5 == expected

expect = Expect()
expected = 0
multiple_of_5 = expect.should(MultipleOf5, expected)

assert multiple_of_5(10)
assert multiple_of_5(11) is False

# Should provides also the negation:
not_multiple_of_5 = expect.should_not(MultipleOf5, expected)

assert not_multiple_of_5(11)

# Should can take closure:
divide_by_2 = lambda given: given / 2
multiple_of_2_and_5 = expect.should(MultipleOf5, expected, divide_by_2)

assert multiple_of_2_and_5(10)
assert multiple_of_2_and_5(15) is False

# Should syntactic sugar:
is_10 = expect.should == 10
assert is_10(10)
assert is_10(11) is False
# like expect:
is_10 = expect == 10
assert is_10(10)
assert is_10(11) is False

# at the difference that should can take a closure:
mod_2 = lambda num: num % 2
multiple_of_2 = expect.should == (0, mod_2)
assert multiple_of_2(10)
assert multiple_of_2(11) is False

# unlike expect:
weird_example = expect == (0, mod_2)
assert weird_example(10) is False
assert weird_example((0, mod_2))


Fell free to give feedback or improvements.

Launch test:

git clone
cd inxpect
nosetests --with-spec --spec-color

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