CODEWITHSUNDEEP
pythontimewhile-looptimercountdown
luke
luke

Reputation: 207

How do I make a while loop print a result just once, unless the result changes?

I've made a short countdown program which starts at 4 and counts down to zero, I'd like this countdown to print each number just once before moving on to the next number (i.e 4,3,2,1,0), but it currently prints each number multiple times.

This is my Code:

import time

def timer():
    
    max_time = 4
    start_time = time.time()
    while max_time > 0:
        difference = time.time() - start_time

        if 1 > difference > 0:
            print(max_time)
        
        if 2 > difference > 1:
            max_time = 3
            print(max_time)
        
        elif 3 > difference > 2:
            max_time = 2
            print(max_time)
        
        elif 4 > difference > 3:
            max_time = 1
            print(max_time)
        
        elif 5 > difference > 4:
            print('Go')
            break
            
timer()

Currently I get a result like this:

4
4
4
4
3
3
3
3
2
2
2
2
1
1
1
1

Where I'd like a result like this:

4
3
2
1

Thanks

Upvotes: 0

Views: 70

Answers (2)

Pi Marillion
Pi Marillion

Reputation: 4674

To answer your explicit question about a print once type of function: I'd use a class that remembers the last thing printed. It's important to use a context manager (with expression) here, since the last line printed won't necessarily be garbage collected when you're done with it otherwise.

class Printer:
    '''Prints only changed lines'''

    def __init__(self):
        # a new, unique object() is never equal to anything else
        self._last = object()

    def __enter__(self):
        # let with...as statement get to print_once() directly
        return self.print_once

    def __exit__(self, *_):
        # let the last line be garbage collected
        del self._last

    def print_once(self, line):
        '''Print onlt changed line'''
        # don't print the same thing again
        if line != self._last:
            # print the unique thing
            print(line)
            # remember the last thing printed
            self._last = line

with Printer() as print_once:
    for line in [4, 4, 4, 4, 3, 3, 3, 3, 2, 2, 2, 2, 1, 1, 1, 1]:
        print_once(line)

If, instead, you just want something to count down from 4 once a second, then refer to Tim Roberts' answer. ;)

Upvotes: 0

Tim Roberts
Tim Roberts

Reputation: 54645

Your code consumes 100% of a CPU. That's wasteful. You do a timer by putting yourself to sleep for a while:

import time

def timer():
    max_time = 4
    for i in range(max_time,0,-1):
        print(i)
        time.sleep(1)
    print('Go')
      
timer()

Upvotes: 1

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