def read(self, num):
r"""
Reads `num` elements from the file and return the result as a
numpy matrix. Last read is truncated.
Tests:
>>> f = FTFile('/data/lisa/data/nist/by_class/digits/digits_test_labels.ft')
>>> f.read(1)
array([6], dtype=int32)
>>> f.read(10)
array([7, 4, 7, 5, 6, 4, 8, 0, 9, 6], dtype=int32)
>>> f.skip(58630)
>>> f.read(10)
array([9, 2, 4, 2, 8], dtype=int32)
>>> f.read(10)
array([], dtype=int32)
>>> f = FTFile('/data/lisa/data/nist/by_class/digits/digits_test_data.ft')
>>> f.read(1)
array([[0, 0, 0, ..., 0, 0, 0]], dtype=uint8)
"""
if num > self.size:
num = self.size
self.dim[0] = num
self.size -= num
if self.gz:
d = self.file.read(_prod(self.dim)*self.elsize)
res = numpy.fromstring(d, dtype=self.magic_t, count=_prod(self.dim)).reshape(self.dim)
else:
res = numpy.fromfile(self.file, dtype=self.magic_t, count=_prod(self.dim)).reshape(self.dim)
if self.dtype is not None:
res = res.astype(self.dtype)
if self.scale != 1:
res /= self.scale
return res
def skip(self, num):
r"""
Skips `num` items in the file.
If `num` is negative, skips size-num.
Tests:
>>> f = FTFile('/data/lisa/data/nist/by_class/digits/digits_test_labels.ft')
>>> f.size
58646
>>> f.elsize
4
>>> f.file.tell()
20
>>> f.skip(1000)
>>> f.file.tell()
4020
>>> f.size
57646
>>> f = FTFile('/data/lisa/data/nist/by_class/digits/digits_test_labels.ft')
>>> f.size
58646
>>> f.file.tell()
20
>>> f.skip(-1000)
>>> f.file.tell()
230604
>>> f.size
1000
"""
if num < 0:
num += self.size
if num < 0:
raise ValueError('Skipping past the start of the file')
if num >= self.size:
self.size = 0
else:
self.size -= num
f_start = self.file.tell()
self.file.seek(f_start + (self.elsize * _prod(self.dim[1:]) * num))
