Basic API (pyhdf.HDF)

A module of the pyhdf package implementing the basic API of the NCSA HDF4 library.

Introduction

The role of the HDF module is to provide support to other modules of the pyhdf package. It defines constants specifying file opening modes and various data types, methods for accessing files, plus a few utility functions to query library version and check if a file is an HDF one.

It should be noted that, among the modules of the pyhdf package, SD is special in the sense that it is self-contained and does not need support from the HDF module. For example, SD provides its own file opening and closing methods, whereas VS uses methods of the HDF.HDF class for that.

Functions and classes summary

The HDF module provides the following classes.

HC

The HC class holds constants defining opening modes and various data types.

HDF

The HDF class provides methods to open and close an HDF file, and return instances of the major HDF APIs (except SD).

To instantiate an HDF class, call the HDF() constructor.

methods:

constructors:

HDF() open an HDF file, creating the file if necessary,

and return an HDF instance

vstart() initialize the VS (Vdata) API over the HDF file and

return a VS instance

vgstart() initialize the V (Vgroup) interface over the HDF file

and return a V instance.

closing file

close() close the HDF file

inquiry

getfileversion() return info about the version of the HDF file

The HDF module also offers the following functions.

inquiry

getlibversion() return info about the version of the library ishdf() determine whether a file is an HDF file

class pyhdf.HDF.HDF(path, mode=1, nblocks=0)

The HDF class encapsulates the basic HDF functions. Its main use is to open and close an HDF file, and return instances of the major HDF APIs (except for SD). To instantiate an HDF class, call the HDF() constructor.

close()

Close the HDF file.

Args:

no argument

Returns:

None

C library equivalent : Hclose

getfileversion()

Get file version info.

Args:

no argument

Returns:

4-element tuple with the following components:

-major version number (int) -minor version number (int) -complete library version number (int) -additional information (string)

C library equivalent : Hgetlibversion

vgstart()

Initialize the V API over the file and return a V instance.

Args:

no argument

Returns:

V instance

C library equivalent : Vstart (in fact: Vinitialize)

vstart()

Initialize the VS API over the file and return a VS instance.

Args:

no argument

Returns:

VS instance

C library equivalent : Vstart (in fact: Vinitialize)

exception pyhdf.HDF.HDF4Error

An error from inside the HDF4 library.

class pyhdf.HDF.HC

The HC class holds constants defining opening modes and data types.

File opening modes (flags ORed together)

CREATE 4 create file if it does not exist READ 1 read-only mode TRUNC 256 truncate if it exists WRITE 2 read-write mode

Data types

CHAR 4 8-bit char CHAR8 4 8-bit char UCHAR 3 unsigned 8-bit integer (0 to 255) UCHAR8 3 unsigned 8-bit integer (0 to 255) INT8 20 signed 8-bit integer (-128 to 127) UINT8 21 unsigned 8-bit integer (0 to 255) INT16 23 signed 16-bit integer UINT16 23 unsigned 16-bit integer INT32 24 signed 32-bit integer UINT32 25 unsigned 32-bit integer FLOAT32 5 32-bit floating point FLOAT64 6 64-bit floating point

Tags

DFTAG_NDG 720 dataset DFTAG_VH 1962 vdata DFTAG_VG 1965 vgroup

CHAR = 4

CHAR8 = 4

CREATE = 4

DFTAG_NDG = 720

DFTAG_VG = 1965

DFTAG_VH = 1962

FLOAT32 = 5

FLOAT64 = 6

FULL_INTERLACE = 0

INT16 = 22

INT32 = 24

INT8 = 20

NO_INTERLACE = 1

READ = 1

TRUNC = 256

UCHAR = 3

UCHAR8 = 3

UINT16 = 23

UINT32 = 25

UINT8 = 21

WRITE = 2

pyhdf.HDF.getlibversion()

Get the library version info.

Args:

no argument

Returns:

4-element tuple with the following components:

-major version number (int) -minor version number (int) -complete library version number (int) -additional information (string)

C library equivalent : Hgetlibversion

pyhdf.HDF.ishdf(filename)

Determine whether a file is an HDF file.

Args:

filename name of the file to check

Returns:

1 if the file is an HDF file, 0 otherwise

C library equivalent : Hishdf