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chapter7: Support both Python 2 and Python 3 #6

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chapter7: Support both Python 2 and Python 3 #6

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5 changes: 3 additions & 2 deletions src/chapter7/breakfast.py
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Original file line number Diff line number Diff line change
@@ -1,10 +1,11 @@
from __future__ import print_function
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Hi @cclauss actually jython supports print() without the import from __future__, at least in 2.7

C:\Users\Adam\jython\jython4>dist\bin\jython.exe
Jython 2.7.2a1+ (, May 9 2019, 11:51:47)
[OpenJDK 64-Bit Server VM (Oracle Corporation)] on java11.0.1
Type "help", "copyright", "credits" or "license" for more information.
>>> print('hi')
hi
>>>

That should make the change less verbose. Thanks for taking the time to submit this and the other v3 compatibility PRs.

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@cclauss cclauss May 15, 2019 •
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Python porting best practice says that we should prevent compatibility regressions. This import changes the way that Python 2 operates so that print statements are now syntax errors while print() function continues to work as expected. This prevents Python 2 developers from writing code that breaks compatibility with Python 3.

Proof:

  • $ python2 -c "print 'This works...'"
  • $ python2 -c "from __future__ import print_function ; print '...but this raises a syntax error.'"

The import is also required in any print statement that contains an unquoted comma.

$ python2

>>> print "hello", "world"
hello world
>>> print("hello", "world")
('hello', 'world')

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Thank you for explaining. I can see the systematic logic to this and understand why it is in the porting guidelines now. I think there is still a decision around its impact on inline explanations in a reference book, as Jeff points out.

While on the topic it is also unfortunately a jython bug with __future__.print_function() when using from an interactive console which might compound confusion.

https://bugs.jython.org/issue2007

class Spam(object):

def order(self, number):
print "spam " * number
print("spam " * number)

def order_eggs():
print " and eggs!"
print(" and eggs!")

s = Spam()
s.order(3)
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3 changes: 2 additions & 1 deletion src/chapter7/greet/__init__.py
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Original file line number Diff line number Diff line change
@@ -1 +1,2 @@
print "in greet/__init__.py"
from __future__ import print_function
print("in greet/__init__.py")
5 changes: 3 additions & 2 deletions src/chapter7/greet/hello.py
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Original file line number Diff line number Diff line change
@@ -1,7 +1,8 @@
print "in greet/hello.py"
from __future__ import print_function
print("in greet/hello.py")
import people

class Greeter(object):
def hello_all(self):
for name in people.names:
print "hello %s" % name
print("hello %s" % name)
3 changes: 2 additions & 1 deletion src/chapter7/greet/people.py
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Original file line number Diff line number Diff line change
@@ -1,3 +1,4 @@
print "in greet/people.py"
from __future__ import print_function
print("in greet/people.py")

names = ["Josh", "Jim", "Victor", "Leo", "Frank"]
3 changes: 2 additions & 1 deletion src/chapter7/greetings.py
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@@ -1,4 +1,5 @@
print "in greeting.py"
from __future__ import print_function
print("in greeting.py")
import greet.hello

g = greet.hello.Greeter()
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