I have been doing some coding in Python recently. While playing around with some code, I noticed that the way heredocs are used in Python is different from Ruby.

Python

Consider the following snippet:

# test.py

print "some text in single line"

print """
As opposed to
some text
written as
heredoc
"""
print "and then another single line"

When run, this would result in this:

bash-3.2$ python test.py
some text in single line

As opposed to
some text
written as
heredoc

and then another single line

Notice how there is a preceding and trailing linebreak around the string printed using heredoc.

I spent a lot of time trying to figure out how and why this was happening. Finally, help came from @dibb on #python. Looks like I was doing it wrong. In Python, the useful part of the heredoc starts immediately after the """. So if you don’t want those excess linebreaks, you should write something like this:

# test2.py

print "some text in single line"

print """As opposed to
some text
written as
heredoc"""

print "and then another single line"

When run, this would print the text without the extra line breaks:

bash-3.2$ python test2.py
some text in single line
As opposed to
some text
written as
heredoc
and then another single line

If you don’t want to write the string just after the """, you could use a \ to remove the linebreaks, like this:

# test3.py

print """\
As opposed to
some text
written as
heredoc\
"""

Ruby

I come from the Ruby world, where the heredocs behave in a slightly different way. The equivalent code in Ruby would look like this:

# test.rb

puts "some text in single line"

puts <<-STR
As opposed to
some text
written as
heredoc
STR

puts "and then another single line"

Notice how the actual content of the heredoc begins only on the line after <<-STR

I hope being aware of this detail saves you some time.

If you have questions or comments about this blog post, you can get in touch with me on Twitter @sdqali.

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