Supported data types in PyTables¶
All PyTables datasets can handle the complete set of data types supported by the NumPy (see [NUMPY]) package in Python. The data types for table fields can be set via instances of the Col class and its descendants (see The Col class and its descendants), while the data type of array elements can be set through the use of the Atom class and its descendants (see The Atom class and its descendants).
PyTables uses ordinary strings to represent its types, with most of them matching the names of NumPy scalar types. Usually, a PyTables type consists of two parts: a kind and a precision in bits. The precision may be omitted in types with just one supported precision (like bool) or with a nonfixed size (like string).
There are eight kinds of types supported by PyTables:
bool: Boolean (true/false) types. Supported precisions: 8 (default) bits.
int: Signed integer types. Supported precisions: 8, 16, 32 (default) and 64 bits.
uint: Unsigned integer types. Supported precisions: 8, 16, 32 (default) and 64 bits.
float: Floating point types. Supported precisions: 16, 32, 64 (default) bits and extended precision floating point (see note on floating point types).
complex: Complex number types. Supported precisions: 64 (32+32), 128 (64+64, default) bits and extended precision complex (see note on floating point types).
string: Raw string types. Supported precisions: 8bit positive multiples.
time: Data/time types. Supported precisions: 32 and 64 (default) bits.
enum: Enumerated types. Precision depends on base type.
Note
Floating point types.
The half precision floating point data type (float16) and extended precision ones (fload96, float128, complex192, complex256) are only available if numpy supports them on the host platform.
Also, in order to use the half precision floating point type (float16) it is required numpy >= 1.6.0.
The time and enum kinds area little bit special, since they represent HDF5 types which have no direct Python counterpart, though atoms of these kinds have a moreorless equivalent NumPy data type.
There are two types of time: 4byte signed integer (time32) and 8byte double precision floating point (time64). Both of them reflect the number of seconds since the Unix epoch, i.e. Jan 1 00:00:00 UTC 1970. They are stored in memory as NumPy’s int32 and float64, respectively, and in the HDF5 file using the H5T_TIME class. Integer times are stored on disk as such, while floating point times are split into two signed integer values representing seconds and microseconds (beware: smaller decimals will be lost!).
PyTables also supports HDF5 H5T_ENUM enumerations (restricted sets of unique name and unique value pairs). The NumPy representation of an enumerated value (an Enum, see The Enum class) depends on the concrete base type used to store the enumeration in the HDF5 file. Currently, only scalar integer values (both signed and unsigned) are supported in enumerations. This restriction may be lifted when HDF5 supports other kinds on enumerated values.
Here you have a quick reference to the complete set of supported data types:
Type Code 
Description 
C Type 
Size (in bytes) 
Python Counterpart 

bool 
boolean 
unsigned char 
1 
bool 
int8 
8bit integer 
signed char 
1 
int 
uint8 
8bit unsigned integer 
unsigned char 
1 
int 
int16 
16bit integer 
short 
2 
int 
uint16 
16bit unsigned integer 
unsigned short 
2 
int 
int32 
integer 
int 
4 
int 
uint32 
unsigned integer 
unsigned int 
4 
long 
int64 
64bit integer 
long long 
8 
long 
uint64 
unsigned 64bit integer 
unsigned long long 
8 
long 
float16 [1] 
halfprecision float 
2 

float32 
singleprecision float 
float 
4 
float 
float64 
doubleprecision float 
double 
8 
float 
extended precision float 
12 

extended precision float 
16 

complex64 
singleprecision complex 
struct {float r, i;} 
8 
complex 
complex128 
doubleprecision complex 
struct {double r, i;} 
16 
complex 
complex192 [1] 
extended precision complex 
24 

complex256 [1] 
extended precision complex 
32 

string 
arbitrary length string 
char[] 
str 

time32 
integer time 
POSIX’s time_t 
4 
int 
time64 
floating point time 
POSIX’s struct timeval 
8 
float 
enum 
enumerated value 
enum 
Footnotes