Python Assign value to variable during condition in while Loop

Question

A simple question about Python syntax. I want to assign a value from a function to a variable during the condition for a while loop. When the value returned from the function is false, the loop should break. I know how to do it in PHP.

while (($data = fgetcsv($fh, 1000, ",")) !== FALSE)  

However when I try a similar syntax in Python I get a syntax error.

Answer 1

2020 answer:

Since Python 3.8, the "walrus operator" := exists that does exactly what you want:

while data := fgetcsv(fh, 1000, ",") != False:     pass 

(if that fgetcsv function existed)

2013 answer: You can't do that in Python, no assignment in expressions. At least that means you won't accidentally type == instead of = or the other way around and have it work.

Traditional Python style is to just use while True and break:

while True:     data = fgetcsv(fh, 1000, ",")     if not data:         break     # Use data here 

But nowadays I'd put that in a generator:

def data_parts(fh):     while True:         data = fgetcsv(fh, 1000, ",")         if not data:             break         yield data 

so that in the code that uses the file, the ugliness is hidden away:

for data in data_parts(fh):     # Use data here 

Of course if it's actually CSV reading that you're doing, use the csv module.