I am trying to read a string of bytes from a file using NumPy fromfile
in Python 3. My goal is to convert the bytes to a normal Python 3 string. For example:
$ echo "1234" > t.txt
Now the file t.txt
contains 4 bytes of text. Then:
import numpy as np
values=np.fromfile('t.txt',dtype='|S1',count=4)
print ("values={}".format(values))
values=np.fromfile('t.txt',dtype='|U1',count=4)
print ("values={}".format(values))
gives:
values=[b'1' b'2' b'3' b'4']
Traceback (most recent call last):
File "./t.py", line 12, in <module>
print ("values={}".format(values))
File "/home/hakon/.pyenv/versions/3.4.2/lib/python3.4/site-packages/numpy/core/numeric.py", line 1715, in array_str
return array2string(a, max_line_width, precision, suppress_small, ' ', "", str)
File "/home/hakon/.pyenv/versions/3.4.2/lib/python3.4/site-packages/numpy/core/arrayprint.py", line 454, in array2string
separator, prefix, formatter=formatter)
File "/home/hakon/.pyenv/versions/3.4.2/lib/python3.4/site-packages/numpy/core/arrayprint.py", line 328, in _array2string
_summaryEdgeItems, summary_insert)[:-1]
File "/home/hakon/.pyenv/versions/3.4.2/lib/python3.4/site-packages/numpy/core/arrayprint.py", line 500, in _formatArray
word = format_function(a[-1])
UnicodeDecodeError: 'utf-32-le' codec can't decode bytes in position 0-3: codepoint not in range(0x110000)
I would like to obtain a normal Python 3 string like values='1234'
. How can this be done?
You could use astype
to convert the bytes to str:
import numpy as np
values = np.fromfile('t.txt',dtype='|S1',count=4).astype('|U1')
print(values)
# ['1' '2' '3' '4']
print(values.view('|U4'))
# ['1234']
print(values.dtype)
# <U1
I know the question explicitly asks for np.fromfile
, but why not simply use the built-in file interface directly?
f = open('t.txt', 'r')
values = f.read().rstrip('\n')
f.close()
Note: Python 3 strings are Unicode by default.
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