# Concrete Objects Layer {#concrete}

The functions in this chapter are specific to certain Python object types. Passing them an object of the wrong type is not a good idea; if you receive an object from a Python program and you are not sure that it has the right type, you must perform a type check first; for example, to check that an object is a dictionary, use `PyDict_Check`{.interpreted-text role="c:func"}. The chapter is structured like the \"family tree\" of Python object types.

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Warning
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While the functions described in this chapter carefully check the type of the objects which are passed in, many of them do not check for `NULL` being passed instead of a valid object. Allowing `NULL` to be passed in can cause memory access violations and immediate termination of the interpreter.
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## Fundamental Objects {#fundamental}

This section describes Python type objects and the singleton object `None`.

::: toctree
type.rst none.rst
:::

## Numeric Objects {#numericobjects}

::: index
pair: object; numeric
:::

::: toctree
long.rst bool.rst float.rst complex.rst
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## Sequence Objects {#sequenceobjects}

::: index
pair: object; sequence
:::

Generic operations on sequence objects were discussed in the previous chapter; this section deals with the specific kinds of sequence objects that are intrinsic to the Python language.

::: toctree
bytes.rst bytearray.rst unicode.rst tuple.rst list.rst
:::

## Container Objects {#mapobjects}

::: index
pair: object; mapping
:::

::: toctree
dict.rst set.rst
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## Function Objects {#otherobjects}

::: toctree
function.rst method.rst cell.rst code.rst
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## Other Objects

::: toctree
file.rst module.rst iterator.rst descriptor.rst slice.rst memoryview.rst picklebuffer.rst weakref.rst capsule.rst frame.rst gen.rst coro.rst contextvars.rst typehints.rst
:::

## C API for extension modules

::: toctree
curses.rst datetime.rst
:::