Assignment Condition in Python While Loop

Question

In C, one can do

while( (i=a) != b ) { } 

but in Python, it appears, one cannot.

while (i = sys.stdin.read(1)) != "\n": 

generates

    while (i = sys.stdin.read(1)) != "\n":          ^ SyntaxError: invalid syntax 

(the ^ should be on the =)

Is there a workaround?

Answer 1

Starting Python 3.8, and the introduction of assignment expressions (PEP 572) (:= operator), it's now possible to capture an expression value (here sys.stdin.read(1)) as a variable in order to use it within the body of while:

while (i := sys.stdin.read(1)) != '\n':   do_smthg(i) 

This:

• Assigns sys.stdin.read(1) to a variable i
• Compares i to \n
• If the condition is validated, enters the while body in which i can be used

Answer 2

Use break:

while True:     i = sys.stdin.read(1)     if i == "\n":        break     # etc...