round() returns different result depending on the number of arguments

up vote
20
down vote

favorite

While using the round() function I noticed that I get two different results depending on whether I don't explicitly choose the number of decimal places to include or choosing the number to be 0.

x = 4.1
print(round(x))
print(round(x, 0))

It prints the following:

4
4.0

What is the difference?

edited 12 mins ago

Aran-Fey

20.3k53166

asked 8 hours ago

Peter Hofer

1144

New contributor

1

I get 4.0 in both cases (python 3.5)
â€“Â taras
8 hours ago

5

+1 I was surprised by the downvote. This is a good question, with runnable code, probing a counterintuitive edge-case. I certainly learned something from this. Thanks, Peter.
â€“Â Bill Cheatham
8 hours ago

6

@taras: nope, round(4.1) in Python 3.5 produces 4, only round(4.1, 0) produces 4.0. Do triple-check your Python versions. Use import sys; print(sys.version_info) from inside Python if you have to, because the behaviour you are reporting is specific to Python two. The round() function documentation for Python 3 covers this case explicitly: If ndigits is omitted or is None, it returns the nearest integer to its input..
â€“Â Martijn Pietersâ™¦
8 hours ago

1

@MartijnPieters, thank you for pointing it out. Apparently, I've checked it using 2.7 thinking I was running 3.5.
â€“Â taras
7 hours ago

How is this not a duplicate after more than 10 years and more than 15 million questions?
â€“Â Peter Mortensen
2 hours ago

add a commentÂ |Â

up vote
20
down vote

favorite

While using the round() function I noticed that I get two different results depending on whether I don't explicitly choose the number of decimal places to include or choosing the number to be 0.

x = 4.1
print(round(x))
print(round(x, 0))

It prints the following:

4
4.0

What is the difference?

edited 12 mins ago

Aran-Fey

20.3k53166

asked 8 hours ago

Peter Hofer

1144

New contributor

1

I get 4.0 in both cases (python 3.5)
â€“Â taras
8 hours ago

5

+1 I was surprised by the downvote. This is a good question, with runnable code, probing a counterintuitive edge-case. I certainly learned something from this. Thanks, Peter.
â€“Â Bill Cheatham
8 hours ago

6

@taras: nope, round(4.1) in Python 3.5 produces 4, only round(4.1, 0) produces 4.0. Do triple-check your Python versions. Use import sys; print(sys.version_info) from inside Python if you have to, because the behaviour you are reporting is specific to Python two. The round() function documentation for Python 3 covers this case explicitly: If ndigits is omitted or is None, it returns the nearest integer to its input..
â€“Â Martijn Pietersâ™¦
8 hours ago

1

@MartijnPieters, thank you for pointing it out. Apparently, I've checked it using 2.7 thinking I was running 3.5.
â€“Â taras
7 hours ago

How is this not a duplicate after more than 10 years and more than 15 million questions?
â€“Â Peter Mortensen
2 hours ago

add a commentÂ |Â

up vote
20
down vote

favorite

While using the round() function I noticed that I get two different results depending on whether I don't explicitly choose the number of decimal places to include or choosing the number to be 0.

x = 4.1
print(round(x))
print(round(x, 0))

It prints the following:

4
4.0

What is the difference?

edited 12 mins ago

Aran-Fey

20.3k53166

asked 8 hours ago

Peter Hofer

1144

New contributor

While using the round() function I noticed that I get two different results depending on whether I don't explicitly choose the number of decimal places to include or choosing the number to be 0.

x = 4.1
print(round(x))
print(round(x, 0))

It prints the following:

4
4.0

What is the difference?

python python-3.x rounding

edited 12 mins ago

Aran-Fey

20.3k53166

asked 8 hours ago

Peter Hofer

1144

New contributor

edited 12 mins ago

Aran-Fey

20.3k53166

asked 8 hours ago

Peter Hofer

1144

New contributor

edited 12 mins ago

Aran-Fey

20.3k53166

edited 12 mins ago

Aran-Fey

20.3k53166

edited 12 mins ago

Aran-Fey

20.3k53166

asked 8 hours ago

Peter Hofer

1144

New contributor

asked 8 hours ago

Peter Hofer

1144

asked 8 hours ago

Peter Hofer

1144

New contributor

Peter Hofer is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

1

I get 4.0 in both cases (python 3.5)
â€“Â taras
8 hours ago

5

+1 I was surprised by the downvote. This is a good question, with runnable code, probing a counterintuitive edge-case. I certainly learned something from this. Thanks, Peter.
â€“Â Bill Cheatham
8 hours ago

6

@taras: nope, round(4.1) in Python 3.5 produces 4, only round(4.1, 0) produces 4.0. Do triple-check your Python versions. Use import sys; print(sys.version_info) from inside Python if you have to, because the behaviour you are reporting is specific to Python two. The round() function documentation for Python 3 covers this case explicitly: If ndigits is omitted or is None, it returns the nearest integer to its input..
â€“Â Martijn Pietersâ™¦
8 hours ago

1

@MartijnPieters, thank you for pointing it out. Apparently, I've checked it using 2.7 thinking I was running 3.5.
â€“Â taras
7 hours ago

How is this not a duplicate after more than 10 years and more than 15 million questions?
â€“Â Peter Mortensen
2 hours ago

add a commentÂ |Â

1

I get 4.0 in both cases (python 3.5)
â€“Â taras
8 hours ago

5

+1 I was surprised by the downvote. This is a good question, with runnable code, probing a counterintuitive edge-case. I certainly learned something from this. Thanks, Peter.
â€“Â Bill Cheatham
8 hours ago

6

@taras: nope, round(4.1) in Python 3.5 produces 4, only round(4.1, 0) produces 4.0. Do triple-check your Python versions. Use import sys; print(sys.version_info) from inside Python if you have to, because the behaviour you are reporting is specific to Python two. The round() function documentation for Python 3 covers this case explicitly: If ndigits is omitted or is None, it returns the nearest integer to its input..
â€“Â Martijn Pietersâ™¦
8 hours ago

1

@MartijnPieters, thank you for pointing it out. Apparently, I've checked it using 2.7 thinking I was running 3.5.
â€“Â taras
7 hours ago

How is this not a duplicate after more than 10 years and more than 15 million questions?
â€“Â Peter Mortensen
2 hours ago

I get 4.0 in both cases (python 3.5)
â€“Â taras
8 hours ago

+1 I was surprised by the downvote. This is a good question, with runnable code, probing a counterintuitive edge-case. I certainly learned something from this. Thanks, Peter.
â€“Â Bill Cheatham
8 hours ago

@taras: nope, round(4.1) in Python 3.5 produces 4, only round(4.1, 0) produces 4.0. Do triple-check your Python versions. Use import sys; print(sys.version_info) from inside Python if you have to, because the behaviour you are reporting is specific to Python two. The round() function documentation for Python 3 covers this case explicitly: If ndigits is omitted or is None, it returns the nearest integer to its input..
â€“Â Martijn Pietersâ™¦
8 hours ago

@MartijnPieters, thank you for pointing it out. Apparently, I've checked it using 2.7 thinking I was running 3.5.
â€“Â taras
7 hours ago

How is this not a duplicate after more than 10 years and more than 15 million questions?
â€“Â Peter Mortensen
2 hours ago

add a commentÂ |Â

3 Answers
3

active

oldest

votes

up vote
19
down vote

accepted

The round function returns an integer if the second argument is not specified, else the return value has the same type as that of the first argument:

>>> help(round)
Help on built-in function round in module builtins:

round(number, ndigits=None)
 Round a number to a given precision in decimal digits.

 The return value is an integer if ndigits is omitted or None. Otherwise
 the return value has the same type as the number. ndigits may be negative.

So if the arguments passed are an integer and a zero, the return value will be an integer type:

>>> round(100, 0)
100
>>> round(100, 1)
100

For the sake of completeness:

Negative numbers are used for rounding before the decimal place

>>> round(124638, -2)
124600
>>> round(15432.346, -2)
15400.0

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 7 hours ago

Aniket Navlur

449211

I had no idea you could use negative numbers on round(). Good to know!
â€“Â Daffy
43 mins ago

Huh, really the most important part of the answer here is the Help function, because that would allow anyone to get the answer and so much more.
â€“Â Nicholas Pipitone
30 mins ago

add a commentÂ |Â

up vote
11
down vote

When you specify the number of decimals, even if that number is 0, you are calling the version of the method that returns a float. So it is normal that you get that result.

answered 8 hours ago

Osuman AAA

295111

3

Yep, pretty straightforward. Just like it says in help(round), it "returns an int when called with one argument, otherwise the same type as the number."
â€“Â Kevin
8 hours ago

3

Might want to link to the docs and quote the first sentence.
â€“Â kabanus
8 hours ago

1

"version of the method that returns a float" no overloading or return types around here, it's just an if statement checking for args
â€“Â cat
6 hours ago

add a commentÂ |Â

up vote
1
down vote

The round() function in Python takes two parameters:

number - number to be rounded

number of digits (optional) - the number of digits up to which the given number is to be rounded.

Whenever you use the second parameter, Python automatically converts the data type of the return value to float. If you don't use the second optional parameter then the data type remains an integer.

Therefore, it is 4.0 when the parameter is passed and 4 when it isn't.

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 8 hours ago

codelyzer

164114

This is incorrect. "Whenever you use the second parameter, Python automatically converts the data type of the return value to float.". Please cite sources. In this case, attempting to cite sources will show that the return type behaves as Aniket describes (And cites with Help(round))
â€“Â Nicholas Pipitone
31 mins ago

add a commentÂ |Â

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3 Answers
3

active

oldest

votes

3 Answers
3

active

oldest

votes

up vote
19
down vote

accepted

The round function returns an integer if the second argument is not specified, else the return value has the same type as that of the first argument:

>>> help(round)
Help on built-in function round in module builtins:

round(number, ndigits=None)
 Round a number to a given precision in decimal digits.

 The return value is an integer if ndigits is omitted or None. Otherwise
 the return value has the same type as the number. ndigits may be negative.

So if the arguments passed are an integer and a zero, the return value will be an integer type:

>>> round(100, 0)
100
>>> round(100, 1)
100

For the sake of completeness:

Negative numbers are used for rounding before the decimal place

>>> round(124638, -2)
124600
>>> round(15432.346, -2)
15400.0

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 7 hours ago

Aniket Navlur

449211

I had no idea you could use negative numbers on round(). Good to know!
â€“Â Daffy
43 mins ago

Huh, really the most important part of the answer here is the Help function, because that would allow anyone to get the answer and so much more.
â€“Â Nicholas Pipitone
30 mins ago

add a commentÂ |Â

up vote
19
down vote

accepted

The round function returns an integer if the second argument is not specified, else the return value has the same type as that of the first argument:

>>> help(round)
Help on built-in function round in module builtins:

round(number, ndigits=None)
 Round a number to a given precision in decimal digits.

 The return value is an integer if ndigits is omitted or None. Otherwise
 the return value has the same type as the number. ndigits may be negative.

So if the arguments passed are an integer and a zero, the return value will be an integer type:

>>> round(100, 0)
100
>>> round(100, 1)
100

For the sake of completeness:

Negative numbers are used for rounding before the decimal place

>>> round(124638, -2)
124600
>>> round(15432.346, -2)
15400.0

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 7 hours ago

Aniket Navlur

449211

I had no idea you could use negative numbers on round(). Good to know!
â€“Â Daffy
43 mins ago

Huh, really the most important part of the answer here is the Help function, because that would allow anyone to get the answer and so much more.
â€“Â Nicholas Pipitone
30 mins ago

add a commentÂ |Â

up vote
19
down vote

accepted

The round function returns an integer if the second argument is not specified, else the return value has the same type as that of the first argument:

>>> help(round)
Help on built-in function round in module builtins:

round(number, ndigits=None)
 Round a number to a given precision in decimal digits.

 The return value is an integer if ndigits is omitted or None. Otherwise
 the return value has the same type as the number. ndigits may be negative.

So if the arguments passed are an integer and a zero, the return value will be an integer type:

>>> round(100, 0)
100
>>> round(100, 1)
100

For the sake of completeness:

Negative numbers are used for rounding before the decimal place

>>> round(124638, -2)
124600
>>> round(15432.346, -2)
15400.0

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 7 hours ago

Aniket Navlur

449211

The round function returns an integer if the second argument is not specified, else the return value has the same type as that of the first argument:

>>> help(round)
Help on built-in function round in module builtins:

round(number, ndigits=None)
 Round a number to a given precision in decimal digits.

 The return value is an integer if ndigits is omitted or None. Otherwise
 the return value has the same type as the number. ndigits may be negative.

So if the arguments passed are an integer and a zero, the return value will be an integer type:

>>> round(100, 0)
100
>>> round(100, 1)
100

For the sake of completeness:

Negative numbers are used for rounding before the decimal place

>>> round(124638, -2)
124600
>>> round(15432.346, -2)
15400.0

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 7 hours ago

Aniket Navlur

449211

edited 2 hours ago

Peter Mortensen

13.1k1983111

edited 2 hours ago

Peter Mortensen

13.1k1983111

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 7 hours ago

Aniket Navlur

449211

answered 7 hours ago

Aniket Navlur

449211

answered 7 hours ago

Aniket Navlur

449211

I had no idea you could use negative numbers on round(). Good to know!
â€“Â Daffy
43 mins ago

Huh, really the most important part of the answer here is the Help function, because that would allow anyone to get the answer and so much more.
â€“Â Nicholas Pipitone
30 mins ago

add a commentÂ |Â

I had no idea you could use negative numbers on round(). Good to know!
â€“Â Daffy
43 mins ago

Huh, really the most important part of the answer here is the Help function, because that would allow anyone to get the answer and so much more.
â€“Â Nicholas Pipitone
30 mins ago

I had no idea you could use negative numbers on round(). Good to know!
â€“Â Daffy
43 mins ago

Huh, really the most important part of the answer here is the Help function, because that would allow anyone to get the answer and so much more.
â€“Â Nicholas Pipitone
30 mins ago

add a commentÂ |Â

up vote
11
down vote

When you specify the number of decimals, even if that number is 0, you are calling the version of the method that returns a float. So it is normal that you get that result.

answered 8 hours ago

Osuman AAA

295111

3

Yep, pretty straightforward. Just like it says in help(round), it "returns an int when called with one argument, otherwise the same type as the number."
â€“Â Kevin
8 hours ago

3

Might want to link to the docs and quote the first sentence.
â€“Â kabanus
8 hours ago

1

"version of the method that returns a float" no overloading or return types around here, it's just an if statement checking for args
â€“Â cat
6 hours ago

add a commentÂ |Â

up vote
11
down vote

When you specify the number of decimals, even if that number is 0, you are calling the version of the method that returns a float. So it is normal that you get that result.

answered 8 hours ago

Osuman AAA

295111

3

Yep, pretty straightforward. Just like it says in help(round), it "returns an int when called with one argument, otherwise the same type as the number."
â€“Â Kevin
8 hours ago

3

Might want to link to the docs and quote the first sentence.
â€“Â kabanus
8 hours ago

1

"version of the method that returns a float" no overloading or return types around here, it's just an if statement checking for args
â€“Â cat
6 hours ago

add a commentÂ |Â

up vote
11
down vote

When you specify the number of decimals, even if that number is 0, you are calling the version of the method that returns a float. So it is normal that you get that result.

answered 8 hours ago

Osuman AAA

295111

When you specify the number of decimals, even if that number is 0, you are calling the version of the method that returns a float. So it is normal that you get that result.

answered 8 hours ago

Osuman AAA

295111

answered 8 hours ago

Osuman AAA

295111

answered 8 hours ago

Osuman AAA

295111

answered 8 hours ago

Osuman AAA

295111

3

Yep, pretty straightforward. Just like it says in help(round), it "returns an int when called with one argument, otherwise the same type as the number."
â€“Â Kevin
8 hours ago

3

Might want to link to the docs and quote the first sentence.
â€“Â kabanus
8 hours ago

1

"version of the method that returns a float" no overloading or return types around here, it's just an if statement checking for args
â€“Â cat
6 hours ago

add a commentÂ |Â

3

Yep, pretty straightforward. Just like it says in help(round), it "returns an int when called with one argument, otherwise the same type as the number."
â€“Â Kevin
8 hours ago

3

Might want to link to the docs and quote the first sentence.
â€“Â kabanus
8 hours ago

1

"version of the method that returns a float" no overloading or return types around here, it's just an if statement checking for args
â€“Â cat
6 hours ago

Yep, pretty straightforward. Just like it says in help(round), it "returns an int when called with one argument, otherwise the same type as the number."
â€“Â Kevin
8 hours ago

Might want to link to the docs and quote the first sentence.
â€“Â kabanus
8 hours ago

"version of the method that returns a float" no overloading or return types around here, it's just an if statement checking for args
â€“Â cat
6 hours ago

add a commentÂ |Â

up vote
1
down vote

The round() function in Python takes two parameters:

number - number to be rounded

number of digits (optional) - the number of digits up to which the given number is to be rounded.

Whenever you use the second parameter, Python automatically converts the data type of the return value to float. If you don't use the second optional parameter then the data type remains an integer.

Therefore, it is 4.0 when the parameter is passed and 4 when it isn't.

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 8 hours ago

codelyzer

164114

This is incorrect. "Whenever you use the second parameter, Python automatically converts the data type of the return value to float.". Please cite sources. In this case, attempting to cite sources will show that the return type behaves as Aniket describes (And cites with Help(round))
â€“Â Nicholas Pipitone
31 mins ago

add a commentÂ |Â

up vote
1
down vote

The round() function in Python takes two parameters:

number - number to be rounded

number of digits (optional) - the number of digits up to which the given number is to be rounded.

Whenever you use the second parameter, Python automatically converts the data type of the return value to float. If you don't use the second optional parameter then the data type remains an integer.

Therefore, it is 4.0 when the parameter is passed and 4 when it isn't.

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 8 hours ago

codelyzer

164114

This is incorrect. "Whenever you use the second parameter, Python automatically converts the data type of the return value to float.". Please cite sources. In this case, attempting to cite sources will show that the return type behaves as Aniket describes (And cites with Help(round))
â€“Â Nicholas Pipitone
31 mins ago

add a commentÂ |Â

up vote
1
down vote

The round() function in Python takes two parameters:

number - number to be rounded

number of digits (optional) - the number of digits up to which the given number is to be rounded.

Whenever you use the second parameter, Python automatically converts the data type of the return value to float. If you don't use the second optional parameter then the data type remains an integer.

Therefore, it is 4.0 when the parameter is passed and 4 when it isn't.

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 8 hours ago

codelyzer

164114

The round() function in Python takes two parameters:

number - number to be rounded

number of digits (optional) - the number of digits up to which the given number is to be rounded.

Whenever you use the second parameter, Python automatically converts the data type of the return value to float. If you don't use the second optional parameter then the data type remains an integer.

Therefore, it is 4.0 when the parameter is passed and 4 when it isn't.

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 8 hours ago

codelyzer

164114

edited 2 hours ago

Peter Mortensen

13.1k1983111

edited 2 hours ago

Peter Mortensen

13.1k1983111

edited 2 hours ago

Peter Mortensen

13.1k1983111

answered 8 hours ago

codelyzer

164114

answered 8 hours ago

codelyzer

164114

answered 8 hours ago

codelyzer

164114

This is incorrect. "Whenever you use the second parameter, Python automatically converts the data type of the return value to float.". Please cite sources. In this case, attempting to cite sources will show that the return type behaves as Aniket describes (And cites with Help(round))
â€“Â Nicholas Pipitone
31 mins ago

add a commentÂ |Â

This is incorrect. "Whenever you use the second parameter, Python automatically converts the data type of the return value to float.". Please cite sources. In this case, attempting to cite sources will show that the return type behaves as Aniket describes (And cites with Help(round))
â€“Â Nicholas Pipitone
31 mins ago

This is incorrect. "Whenever you use the second parameter, Python automatically converts the data type of the return value to float.". Please cite sources. In this case, attempting to cite sources will show that the return type behaves as Aniket describes (And cites with Help(round))
â€“Â Nicholas Pipitone
31 mins ago

add a commentÂ |Â

Peter Hofer is a new contributor. Be nice, and check out our Code of Conduct.

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