CODEWITHSUNDEEP
pythonpython-3.xbytestring-formattingpython-3.4
CforLinux
CforLinux

Reputation: 309

formatting bytes string into another bytes string

I have a list of bytes strings that I try for format into another string, which in turn I convert to bytes, looks something like this:

byte_string = b'text'
fmt = 'this is the text: %s'
fmt_string = bytes(fmt % byte_string, 'utf-8')

but if I print fmt_string I get this

b"this is the text: b'text'"

I know that in python3.5 I can do this:

b'this is the text: %s' % b'text'

and receive:

b'this is the text: text'

is there a way to do the same with python3.4?

Upvotes: 2

Views: 2006

Answers (1)

Martijn Pieters
Martijn Pieters

Reputation: 1121186

You can't use formatting on bytes objects in Python 3.4 or below. Your options are to upgrade to 3.5 or newer, or not use formatting on bytes.

In Python 3.5 and up, you need to make fmt a bytes object; you'd use a bytes literal, and apply the % operator to that:

fmt = b'this is the text: %s'
fmt_string = fmt % byte_string

Alternatively, encode the template first, then apply the values:

fmt = 'this is the text: %s'
fmt_string = bytes(fmt, 'utf-8') % byte_string

If upgrading is not an option, but your bytes values have a consistent encoding, decode first, then encode again:

fmt = 'this is the text: %s'
fmt_string = bytes(fmt % byte_string.decode('utf-8'), 'utf-8')

If you can't decode your bytes values, then your only remaining option is to concatenate bytes objects:

fmt = b'this is the text: '  # no placeholder
fmt_string = fmt + byte_string

This will require multiple parts if there is text after the placeholders, of course.

Upvotes: 2

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