python的打印功能不完全是普通的功能吗？

Question

Environment: python 2.x

If print is a built-in function, why does it not behave like other functions ? What is so special about print ?

-----------start session--------------
>>> ord 'a'
Exception : invalid syntax
>>> ord('a')
97
>>> print 'a'
a
>>> print('a') 
a
>>> ord
<built-in function ord>
>>> print

-----------finish session--------------

Answer 1

print in Python versions below 3, is not a function. There's a separate print statement which is part of the language grammar. print is not an identifier. It's a keyword.

Answer 2

The short answer is that in Python 2, print is not a function but a statement .

In all versions of Python, almost everything is an object. All objects have a type. We can discover an object's type by applying the type function to the object.

Using the interpreter we can see that the builtin functions sum and ord are exactly that in Python's type system:

>>> type(sum)
<type 'builtin_function_or_method'>
>>> type(ord)
<type 'builtin_function_or_method'>

But the following expression is not even valid Python:

>>> type(print)
SyntaxError: invalid syntax

This is because the name print itself is a keyword, like if or return . Keywords are not objects.

The more complete answer is that print can be either a statement or a function depending on the context.

In Python 3, print is no longer a statement but a function .

In Python 2, you can replace the print statement in a module with the equivalent of Python 3's print function by including this statement at the top of the module:

from __future__ import print_function

This special import is available only in Python 2.6 and above.

Refer to the documentation links in my answer for a more complete explanation.

Answer 3

The deal is that print is built-in function only starting from python 3 branch. Looks like you are using python2.

Check out:

print "foo"; # Works in python2, not in python3
print("foo"); # Works in python3

Answer 4

print is more treated like a keyword than a function in python. The parser "knows" the special syntax of print (no parenthesis around the argument) and how to deal with it. I think the Python creator wanted to keep the syntax simple by doing so. As maverik already mentioned, in python3 print is being called like any other function and a syntx error is being thrown if you do it the old way.