How to create a switching function in Python?

Question

I'm having difficulty creating a program that switches between string "X" and "O" every time the function is ran.

So for example, the first time switcher() is ran, it prints "x," and the next time it runs, it prints "o," and third it prints "x," and so forth

I've been able to achieve this without a function and just using an if else loop, but I can't do it using a function

def switch(value):
    if value == 0:
        x = value
        x + 1
        print("value: " + str(x) + " | turn: x")
        return x
    else:
        print("o")
        return 0

x = 0
for i in range(4):
    switch(x)

it outputs:

value: 0 | turn: x
value: 0 | turn: x
value: 0 | turn: x
value: 0 | turn: x

In order to achieve this, I make it so that when x = 0, it prints "X" and when it's 1 it prints "O," and then resets back to 0. It stays as 0 and only gives me x.

You were close, but forgot to update x in your for loop: x = switch(x) — Anthony
– Anthony, Commented May 31, 2019 at 23:55
@RooThaDude, I added an answer to your question. Hopefully, any of the alternatives I am adding will help you. — lmiguelvargasf
– lmiguelvargasf, Commented Jun 1, 2019 at 0:23
Possible duplicate of Python: How to toggle between two values — Dave Liu
– Dave Liu, Commented Jun 1, 2019 at 0:24

Jab · Accepted Answer · 2019-06-01 00:47:14Z

Using cycle from itertools

I think a good approach is to use the function cycle in itertools

from itertools import cycle

def switch():
    return cycle(["X", "O"])

i = 0
for output in switch():
    i += 1
    print(output)
    if i == 5:
        break

Output:

X
O
X
O
X

Using a global variable

You can also use a global variable to keep track of the last generated value. However, it is not a good idea to use a global variable.

last_value = None

def switch():
    global last_value
    if last_value in (None, "O"):
        last_value = "X"
        return "X"
    last_value = "O"
    return "O"

for _ in range(5):
    print(switch())

Output:

'X'
'O'
'X'
'O'
'X'

Using a local variable

You can also pass a parameter that indicates the last value that was returned.

def switch(last_value):
    if last_value in (None, "O"):
        return "X"
    return "O"

last_value = None
for _ in range(5):
    last_value = switch(last_value)
    print(last_value)

Output:

X
O
X
O
x

Sachin Dangol · Accepted Answer · 2019-06-06 13:05:54Z

1

Probably most fun and simple use case of Clousers. Concept works in many other programming languages including javascript, perl etc and even syntax is almost same:

def switch():
    string = 'o'
    def change():
        nonlocal string
        if(string == 'x'):
            string = 'o'
        else:
            string = 'x'
        return string

    return change

switcher = switch()
for _ in range(4):
    print(switcher())

output:

x
o
x
o

edited Jun 6, 2019 at 13:05

answered Jun 1, 2019 at 0:59

Sachin Dangol

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Comments

Perplexabot · Accepted Answer · 2019-05-31 23:52:38Z

0

Is this what you are looking for:

class switcher:
    def __init__(self):
        self.cnt = -1

    def switch(self):
        self.cnt += 1
        return '0' if self.cnt % 2 else '1'


mySwitch = switcher().switch

print(mySwitch())
print(mySwitch())
print(mySwitch())
print(mySwitch())

This will print:

There are other methods to achieve this, like using decorators.

answered May 31, 2019 at 23:52

Perplexabot

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Comments

Jab · Accepted Answer · 2019-06-01 00:45:31Z

0

You could use boolean indexing:

def switch(options=('X', 'O')):
    val = False
    while True:
        val = not val
        yield options[val]

switcher = switch()
for _ in range(5):
    print(next(switcher))

This prints:

O
X
O
X
O

answered Jun 1, 2019 at 0:45

Jab

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Comments

enjoyingthis · Accepted Answer · 2019-06-01 01:17:19Z

0

You could do something like this...works pretty well:

def switch(count):
    x = 0
    z = 1
    y = 0
    value = 1
    while x < count:
        if value == z:
            print(y)
            value = 0
        elif value == y:
            print(z)
            value = 1
        x+=1

Then: (Based on the count it prints however many alterations)

switch(10)
0
1
0
1
0
1
0
1
0
1

answered Jun 1, 2019 at 1:17

enjoyingthis

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Comments

Masoud · Accepted Answer · 2019-06-01 01:29:05Z

0

You can define an Boolean attribute for the function, toggle it each time the function is called:

def switch(value):
    if switch.state:
        print ('x')
    else:
        print('o')
    switch.state = not switch.state

switch.state = False
for x in range(4):
    switch(x)

answered Jun 1, 2019 at 1:29

Masoud

1,2809 silver badges12 bronze badges

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How to create a switching function in Python?

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Using cycle from itertools

Using a global variable

Using a local variable

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Using cycle from itertools

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