Why we need to check if value equals None?












2















values = [-50, -80, -100]

max_value = None

for i in values:

    if max_value is None or i > max_value:

        max_value = i


why we need to include this code max_value is None
Let's say we go through the for loop
Loop 1: i = -50. We can't evaluate -50 with None, right?






python







share|improve this question


















  • 1





    max_value is set to None and evaluated the first time before it is changed.

    – Michael Butscher
    Nov 25 '18 at 1:06











  • Exactly. Need it there to avoid an error.

    – Anton vBR
    Nov 25 '18 at 1:08











  • So that's only a trick to avoid an error?

    – The One
    Nov 25 '18 at 1:11






  • 2





    @TheOne, You could call it "a trick", but that's not a technical term. It's a way to make your program work, given max_value is initialised as None.

    – jpp
    Nov 25 '18 at 1:21


















2















values = [-50, -80, -100]

max_value = None

for i in values:

    if max_value is None or i > max_value:

        max_value = i


why we need to include this code max_value is None
Let's say we go through the for loop
Loop 1: i = -50. We can't evaluate -50 with None, right?






python







share|improve this question


















  • 1





    max_value is set to None and evaluated the first time before it is changed.

    – Michael Butscher
    Nov 25 '18 at 1:06











  • Exactly. Need it there to avoid an error.

    – Anton vBR
    Nov 25 '18 at 1:08











  • So that's only a trick to avoid an error?

    – The One
    Nov 25 '18 at 1:11






  • 2





    @TheOne, You could call it "a trick", but that's not a technical term. It's a way to make your program work, given max_value is initialised as None.

    – jpp
    Nov 25 '18 at 1:21
















2












2








2








values = [-50, -80, -100]

max_value = None

for i in values:

    if max_value is None or i > max_value:

        max_value = i


why we need to include this code max_value is None
Let's say we go through the for loop
Loop 1: i = -50. We can't evaluate -50 with None, right?






python







share|improve this question














values = [-50, -80, -100]

max_value = None

for i in values:

    if max_value is None or i > max_value:

        max_value = i


why we need to include this code max_value is None
Let's say we go through the for loop
Loop 1: i = -50. We can't evaluate -50 with None, right?






python




python






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 25 '18 at 1:04









The OneThe One

4331520




4331520








  • 1





    max_value is set to None and evaluated the first time before it is changed.

    – Michael Butscher
    Nov 25 '18 at 1:06











  • Exactly. Need it there to avoid an error.

    – Anton vBR
    Nov 25 '18 at 1:08











  • So that's only a trick to avoid an error?

    – The One
    Nov 25 '18 at 1:11






  • 2





    @TheOne, You could call it "a trick", but that's not a technical term. It's a way to make your program work, given max_value is initialised as None.

    – jpp
    Nov 25 '18 at 1:21
















  • 1





    max_value is set to None and evaluated the first time before it is changed.

    – Michael Butscher
    Nov 25 '18 at 1:06











  • Exactly. Need it there to avoid an error.

    – Anton vBR
    Nov 25 '18 at 1:08











  • So that's only a trick to avoid an error?

    – The One
    Nov 25 '18 at 1:11






  • 2





    @TheOne, You could call it "a trick", but that's not a technical term. It's a way to make your program work, given max_value is initialised as None.

    – jpp
    Nov 25 '18 at 1:21










1




1





max_value is set to None and evaluated the first time before it is changed.

– Michael Butscher
Nov 25 '18 at 1:06





max_value is set to None and evaluated the first time before it is changed.

– Michael Butscher
Nov 25 '18 at 1:06













Exactly. Need it there to avoid an error.

– Anton vBR
Nov 25 '18 at 1:08





Exactly. Need it there to avoid an error.

– Anton vBR
Nov 25 '18 at 1:08













So that's only a trick to avoid an error?

– The One
Nov 25 '18 at 1:11





So that's only a trick to avoid an error?

– The One
Nov 25 '18 at 1:11




2




2





@TheOne, You could call it "a trick", but that's not a technical term. It's a way to make your program work, given max_value is initialised as None.

– jpp
Nov 25 '18 at 1:21







@TheOne, You could call it "a trick", but that's not a technical term. It's a way to make your program work, given max_value is initialised as None.

– jpp
Nov 25 '18 at 1:21














2 Answers
2






active

oldest

votes


















1














Because you can't compare int with NoneType, this gives TypeError:



-50 > None  # TypeError: '>' not supported between instances of 'int' and 'NoneType'


So removing the condition will lead your code to break. But, much better, set a minimal starting value, e.g. -inf:



values = [-50, -80, -100]

max_value = -float('inf')

for i in values:

    if i > max_value:

        max_value = i


Of course, for your trivial computation, you can use the built-in max:



max(values)  # -50





share|improve this answer
























  • I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

    – The One
    Nov 25 '18 at 1:17











  • @TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

    – jpp
    Nov 25 '18 at 1:18













  • If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

    – The One
    Nov 25 '18 at 1:25











  • or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

    – jpp
    Nov 25 '18 at 1:26






  • 1





    You will encounter None very often while programming in Python.

    – Matthias
    Nov 25 '18 at 8:26



















1














The most idiomatic approach is to assume values[0] as the maximum and start iterating from the first index:



values = [-50, -80, -100]

max_value = values[0]

for i in values[1:]:

    if i > max_value:

        max_value = i


And you can get rid of the None check.






share|improve this answer
























  • To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

    – The One
    Nov 25 '18 at 1:13











  • @TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

    – coldspeed
    Nov 25 '18 at 1:14











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2 Answers
2






active

oldest

votes








2 Answers
2






active

oldest

votes









active

oldest

votes






active

oldest

votes









1














Because you can't compare int with NoneType, this gives TypeError:



-50 > None  # TypeError: '>' not supported between instances of 'int' and 'NoneType'


So removing the condition will lead your code to break. But, much better, set a minimal starting value, e.g. -inf:



values = [-50, -80, -100]

max_value = -float('inf')

for i in values:

    if i > max_value:

        max_value = i


Of course, for your trivial computation, you can use the built-in max:



max(values)  # -50





share|improve this answer
























  • I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

    – The One
    Nov 25 '18 at 1:17











  • @TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

    – jpp
    Nov 25 '18 at 1:18













  • If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

    – The One
    Nov 25 '18 at 1:25











  • or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

    – jpp
    Nov 25 '18 at 1:26






  • 1





    You will encounter None very often while programming in Python.

    – Matthias
    Nov 25 '18 at 8:26
















1














Because you can't compare int with NoneType, this gives TypeError:



-50 > None  # TypeError: '>' not supported between instances of 'int' and 'NoneType'


So removing the condition will lead your code to break. But, much better, set a minimal starting value, e.g. -inf:



values = [-50, -80, -100]

max_value = -float('inf')

for i in values:

    if i > max_value:

        max_value = i


Of course, for your trivial computation, you can use the built-in max:



max(values)  # -50





share|improve this answer
























  • I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

    – The One
    Nov 25 '18 at 1:17











  • @TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

    – jpp
    Nov 25 '18 at 1:18













  • If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

    – The One
    Nov 25 '18 at 1:25











  • or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

    – jpp
    Nov 25 '18 at 1:26






  • 1





    You will encounter None very often while programming in Python.

    – Matthias
    Nov 25 '18 at 8:26














1












1








1







Because you can't compare int with NoneType, this gives TypeError:



-50 > None  # TypeError: '>' not supported between instances of 'int' and 'NoneType'


So removing the condition will lead your code to break. But, much better, set a minimal starting value, e.g. -inf:



values = [-50, -80, -100]

max_value = -float('inf')

for i in values:

    if i > max_value:

        max_value = i


Of course, for your trivial computation, you can use the built-in max:



max(values)  # -50





share|improve this answer













Because you can't compare int with NoneType, this gives TypeError:



-50 > None  # TypeError: '>' not supported between instances of 'int' and 'NoneType'


So removing the condition will lead your code to break. But, much better, set a minimal starting value, e.g. -inf:



values = [-50, -80, -100]

max_value = -float('inf')

for i in values:

    if i > max_value:

        max_value = i


Of course, for your trivial computation, you can use the built-in max:



max(values)  # -50






share|improve this answer












share|improve this answer



share|improve this answer










answered Nov 25 '18 at 1:07









jppjpp

101k2164114




101k2164114













  • I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

    – The One
    Nov 25 '18 at 1:17











  • @TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

    – jpp
    Nov 25 '18 at 1:18













  • If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

    – The One
    Nov 25 '18 at 1:25











  • or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

    – jpp
    Nov 25 '18 at 1:26






  • 1





    You will encounter None very often while programming in Python.

    – Matthias
    Nov 25 '18 at 8:26



















  • I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

    – The One
    Nov 25 '18 at 1:17











  • @TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

    – jpp
    Nov 25 '18 at 1:18













  • If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

    – The One
    Nov 25 '18 at 1:25











  • or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

    – jpp
    Nov 25 '18 at 1:26






  • 1





    You will encounter None very often while programming in Python.

    – Matthias
    Nov 25 '18 at 8:26

















I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

– The One
Nov 25 '18 at 1:17





I just want to understand about this None. As you said, we can't compare any value to None because it's simpy None so max_value is None here sounds like a trick to me. it doesn't have any meaning as in "i > 3 or i < 10", right?

– The One
Nov 25 '18 at 1:17













@TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

– jpp
Nov 25 '18 at 1:18







@TheOne, Simply put, Python can't evaluate -50 > None, so it gives an error. That makes sense, None isn't a numeric type. So that's why your algorithm checks explicitly first that your value isn't None.

– jpp
Nov 25 '18 at 1:18















If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

– The One
Nov 25 '18 at 1:25





If so, why "if max_value is not None and i > max_value" doesn't give a correct answer?

– The One
Nov 25 '18 at 1:25













or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

– jpp
Nov 25 '18 at 1:26





or is lazy. In the first iteration, the first condition (max_value is not None) is not satisfied, so it moves on to the next. It then tries -50 > None and fails.

– jpp
Nov 25 '18 at 1:26




1




1





You will encounter None very often while programming in Python.

– Matthias
Nov 25 '18 at 8:26





You will encounter None very often while programming in Python.

– Matthias
Nov 25 '18 at 8:26













1














The most idiomatic approach is to assume values[0] as the maximum and start iterating from the first index:



values = [-50, -80, -100]

max_value = values[0]

for i in values[1:]:

    if i > max_value:

        max_value = i


And you can get rid of the None check.






share|improve this answer
























  • To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

    – The One
    Nov 25 '18 at 1:13











  • @TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

    – coldspeed
    Nov 25 '18 at 1:14
















1














The most idiomatic approach is to assume values[0] as the maximum and start iterating from the first index:



values = [-50, -80, -100]

max_value = values[0]

for i in values[1:]:

    if i > max_value:

        max_value = i


And you can get rid of the None check.






share|improve this answer
























  • To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

    – The One
    Nov 25 '18 at 1:13











  • @TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

    – coldspeed
    Nov 25 '18 at 1:14














1












1








1







The most idiomatic approach is to assume values[0] as the maximum and start iterating from the first index:



values = [-50, -80, -100]

max_value = values[0]

for i in values[1:]:

    if i > max_value:

        max_value = i


And you can get rid of the None check.






share|improve this answer













The most idiomatic approach is to assume values[0] as the maximum and start iterating from the first index:



values = [-50, -80, -100]

max_value = values[0]

for i in values[1:]:

    if i > max_value:

        max_value = i


And you can get rid of the None check.







share|improve this answer












share|improve this answer



share|improve this answer










answered Nov 25 '18 at 1:11









coldspeedcoldspeed

135k23145230




135k23145230













  • To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

    – The One
    Nov 25 '18 at 1:13











  • @TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

    – coldspeed
    Nov 25 '18 at 1:14



















  • To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

    – The One
    Nov 25 '18 at 1:13











  • @TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

    – coldspeed
    Nov 25 '18 at 1:14

















To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

– The One
Nov 25 '18 at 1:13





To be honest, i always set the first element in the list as a maximum value. But this None thing confused me.

– The One
Nov 25 '18 at 1:13













@TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

– coldspeed
Nov 25 '18 at 1:14





@TheOne if max_value is None, then i > max_value is not defined. Hence the check. But setting to the first element is the accepted method of initialisation.

– coldspeed
Nov 25 '18 at 1:14


















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