为什么我不能在Python中读取超过16个字节的JPEG文件？

Question

I am trying to read a JPG image in Python.

So far i have:

f = open("test.jpg")
ima = f.read(16)

print "'%s'"% (ima)

It reads 16 bytes and displays the string in console, but it looks like I cannot display more than 32 bytes. Why?

When it tries to read 32 or more bytes, the output will be the same as when it read 16 bytes. Why can I not read more than 16 bytes of the jpeg image?

Answer 1

Two issues here:

1. Set read mode to binary. This way file.read function won't try to convert '\\r\\n' sequences.

2. You're trying to print NULL-terminated string to the console. print function finds first zero character in your string and terminates. Use binascii.hexlify to convert it to the hex:

f = open("test.jpg", "rb")
ima = f.read(16)

print "%s" % (binascii.hexlify(ima))

Answer 2

You probably need to set the open mode to binary:

f = open("test.jpg", "rb") # 'rb' here means "read mode, binary"

See this similar question for a more thorough description.