multiple assignments in a sinlge line python as in Java like a=b=c?

Question

in Java, this is valid. multiple assignments in a single statement.

while ((sCurrentLine = br.readLine()) != null) {
                System.out.println(sCurrentLine);
            }

Is there a similar thing thing in python. I tried but I get the following error.

>>> file = open("reverse.py")
>>> while(x=file.readline()!=""):
  File "<stdin>", line 1
    while(x=file.readline()!=""):
           ^
SyntaxError: invalid syntax

score 4 · Accepted Answer · edited May 23 '17 at 10:32

4

Assignment is not an expression in python. Basically while requires an expression and you are giving an statement.

You can check here for detailed explanation.

edited May 23 '17 at 10:32

Community

1
1

answered Oct 04 '13 at 19:15

moliware

10,160
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+10 internets. This is the important point: Assignment is not an expression but a statement, unlike in many other languages. – Hyperboreus Oct 04 '13 at 19:20
Full definition copied from the docs: expr_stmt: testlist_star_expr (augassign (yield_expr|testlist) | ('=' (yield_expr|testlist_star_expr))*) – Hyperboreus Oct 04 '13 at 19:31

score 0 · Answer 2 · answered Oct 04 '13 at 19:14

0

No, there is no such thing.

On the other hand you don't need this kind of syntax with Python. Just iterate over the file object:

with open(filename) as fp:
    for line in fp:
        pass

answered Oct 04 '13 at 19:14

Matthias

12,873
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There is such a thing. `a = b = c = 42` is valid, normal and everyday python. – Hyperboreus Oct 04 '13 at 19:35

score 0 · Answer 3 · answered Oct 04 '13 at 19:18

multiple assignments work (though maybe not the way you'd expect):

In [373]: a = b = c = 0x1234

In [374]: a
0x1234

In [375]: b
0x1234

In [376]: c
0x1234

your problem is the while syntax, which is just while(predicate). assignments can't be part of a predicate in python.

however, most of the time, you don't need those sorts of constructs in python, as they are implicit. you can do:

file = open('reverse.py')
for line in file:
    <do something>

and it will automatically terminate at EOF with StopIteration; you don't need to do the manual sentinel checks. Even more pythonic would be to use a context manager:

with open('reverse.py') as file:
    for line in file:
        <do something>

which is like the above, but will also automatically close the file when you are done.

multiple assignments in a sinlge line python as in Java like a=b=c?

3 Answers3