Getting Started

Install

pip install assertpy2

Optional extras:

• assertpy2[json] - JSONPath, JSON Schema, and OpenAPI contracts
• assertpy2[inline] - inline snapshots (matches_inline())
• assertpy2[data] - pandas / polars / numpy
• assertpy2[allure] - Allure reporting
• assertpy2[behave] - Behave step matchers

Coming from the original assertpy?

assertpy2 is a drop-in replacement on Python 3.10+. See Migrating from assertpy for the one-line switch and what you gain.

Your first assertion

Wrap a value in assert_that() and chain assertions that read like a sentence:

from assertpy2 import assert_that

assert_that("foobar").is_length(6).starts_with("foo").ends_with("bar")
assert_that([1, 2, 3]).contains(1).does_not_contain(9).is_subset_of([1, 2, 3, 4])

Because every assertion is statically typed, your editor only suggests methods valid for the value's type, and a type checker flags misuse before the test runs. See Type Safety for how the overloads work.

Assertions also return the value they checked, statically narrowed - so you keep using it, correctly typed, with no cast:

# name is typed as str - the value the chain checked
name = assert_that("Alice").is_instance_of(str).is_not_empty().value

When an assertion fails

A failing assertion raises an AssertionError with a precise message:

assert_that(5).is_greater_than(10)
# AssertionError: Expected <5> to be greater than <10>, but was not.

For dicts, dataclasses, and other structures, the pytest plugin renders a path-level diff that points straight at the differing field instead of dumping the whole value:

assert_that(actual).is_equal_to(expected)

The same path-level diff backs matches_structure(), satisfies(), and each(). See Errors & Reporting for the full diff format and configuration.

Collect multiple failures

Use soft assertions to report every failure at once instead of stopping at the first:

from assertpy2 import assert_that, soft_assertions

with soft_assertions():
    assert_that("foo").is_length(3)
    assert_that("foo").starts_with("x")   # collected
    assert_that("foo").ends_with("z")     # collected

Next steps

• Matchers for composable, reusable conditions.
• Fluent API for chaining, negation, and the collection pipeline.
• Browse the assertion reference in the navigation for every type-specific assertion.