If Python does not have a ternary conditional operator, is it possible to simulate one using other language constructs?
This question is related to
python
operators
ternary-operator
conditional-operator
More a tip than an answer (don't need to repeat the obvious for the hundreth time), but I sometimes use it as a oneliner shortcut in such constructs:
if conditionX:
print('yes')
else:
print('nah')
, becomes:
print('yes') if conditionX else print('nah')
Some (many :) may frown upon it as unpythonic (even, ruby-ish :), but I personally find it more natural - i.e. how you'd express it normally, plus a bit more visually appealing in large blocks of code.
is_spacial=True if gender = "Female" else (True if age >= 65 else False)
**
it can be nested as your need. best of luck
**
Ternary conditional operator simply allows testing a condition in a single line replacing the multiline if-else making the code compact.
[on_true] if [expression] else [on_false]
# Program to demonstrate conditional operator
a, b = 10, 20
# Copy value of a in min if a < b else copy b
min = a if a < b else b
print(min) # Output: 10
# Python program to demonstrate ternary operator
a, b = 10, 20
# Use tuple for selecting an item
print( (b, a) [a < b] )
# Use Dictionary for selecting an item
print({True: a, False: b} [a < b])
# lamda is more efficient than above two methods
# because in lambda we are assure that
# only one expression will be evaluated unlike in
# tuple and Dictionary
print((lambda: b, lambda: a)[a < b]()) # in output you should see three 10
# Python program to demonstrate nested ternary operator
a, b = 10, 20
print ("Both a and b are equal" if a == b else "a is greater than b"
if a > b else "b is greater than a")
Above approach can be written as:
# Python program to demonstrate nested ternary operator
a, b = 10, 20
if a != b:
if a > b:
print("a is greater than b")
else:
print("b is greater than a")
else:
print("Both a and b are equal")
# Output: b is greater than a
Simulating the python ternary operator.
For example
a, b, x, y = 1, 2, 'a greather than b', 'b greater than a'
result = (lambda:y, lambda:x)[a > b]()
output:
'b greater than a'
For Python 2.5 and newer there is a specific syntax:
[on_true] if [cond] else [on_false]
In older Pythons a ternary operator is not implemented but it's possible to simulate it.
cond and on_true or on_false
Though, there is a potential problem, which if cond evaluates to True and on_true evaluates to False then on_false is returned instead of on_true. If you want this behavior the method is OK, otherwise use this:
{True: on_true, False: on_false}[cond is True] # is True, not == True
which can be wrapped by:
def q(cond, on_true, on_false)
return {True: on_true, False: on_false}[cond is True]
and used this way:
q(cond, on_true, on_false)
It is compatible with all Python versions.
Does Python have a ternary conditional operator?
Yes. From the grammar file:
test: or_test ['if' or_test 'else' test] | lambdef
The part of interest is:
or_test ['if' or_test 'else' test]
So, a ternary conditional operation is of the form:
expression1 if expression2 else expression3
expression3 will be lazily evaluated (that is, evaluated only if expression2 is false in a boolean context). And because of the recursive definition, you can chain them indefinitely (though it may considered bad style.)
expression1 if expression2 else expression3 if expression4 else expression5 # and so on
Note that every if must be followed with an else. People learning list comprehensions and generator expressions may find this to be a difficult lesson to learn - the following will not work, as Python expects a third expression for an else:
[expression1 if expression2 for element in iterable]
# ^-- need an else here
which raises a SyntaxError: invalid syntax.
So the above is either an incomplete piece of logic (perhaps the user expects a no-op in the false condition) or what may be intended is to use expression2 as a filter - notes that the following is legal Python:
[expression1 for element in iterable if expression2]
expression2 works as a filter for the list comprehension, and is not a ternary conditional operator.
You may find it somewhat painful to write the following:
expression1 if expression1 else expression2
expression1 will have to be evaluated twice with the above usage. It can limit redundancy if it is simply a local variable. However, a common and performant Pythonic idiom for this use-case is to use or's shortcutting behavior:
expression1 or expression2
which is equivalent in semantics. Note that some style-guides may limit this usage on the grounds of clarity - it does pack a lot of meaning into very little syntax.
I find cumbersome the default python syntax val = a if cond else b, so sometimes I do this:
iif = lambda (cond, a, b): a if cond else b
# so I can then use it like:
val = iif(cond, a, b)
Of course, it has the downside of always evaluating both sides (a and b), but the syntax it's way clearer to me
More a tip than an answer (don't need to repeat the obvious for the hundreth time), but I sometimes use it as a oneliner shortcut in such constructs:
if conditionX:
print('yes')
else:
print('nah')
, becomes:
print('yes') if conditionX else print('nah')
Some (many :) may frown upon it as unpythonic (even, ruby-ish :), but I personally find it more natural - i.e. how you'd express it normally, plus a bit more visually appealing in large blocks of code.
Vinko Vrsalovic's answer is good enough. There is only one more thing:
Note that conditionals are an expression, not a statement. This means you can't use assignment statements or
passor other statements within a conditional expression
After that walrus operator was introduced in Python 3.8, there is something changed.
(a := 3) if True else (b := 5)
gives a = 3 and b is not defined,
(a := 3) if False else (b := 5)
gives a is not defined and b = 5, and
c = (a := 3) if False else (b := 5)
gives c = 5, a is not defined and b = 5.
Even if this may be ugly, assignments can be done inside conditional expressions after Python 3.8. Anyway, it is still better to use normal if statement instead in this case.
You might often find
cond and on_true or on_false
but this lead to problem when on_true == 0
>>> x = 0
>>> print x == 0 and 0 or 1
1
>>> x = 1
>>> print x == 0 and 0 or 1
1
where you would expect for a normal ternary operator this result
>>> x = 0
>>> print 0 if x == 0 else 1
0
>>> x = 1
>>> print 0 if x == 0 else 1
1
The ternary operator is a way of writing conditional statements in Python. As the name ternary suggests, this Python operator consists of three operands.
Syntax: The three operands in a ternary operator include:
condition: A boolean expression that evaluates to either true or false.
true_val: A value to be assigned if the expression is evaluated to true.
false_val: A value to be assigned if the expression is evaluated to false.
var = true_val if condition else false_val
The variable var on the left-hand side of the = (assignment) operator will be assigned:
value1 if the booleanExpression evaluates to true.
value2 if the booleanExpression evaluates to false.
Example:
# USING TERNARY OPERATOR
to_check = 6
msg = "Even" if to_check%2 == 0 else "Odd"
print(msg)
# USING USUAL IF-ELSE
msg = ""
if(to_check%2 == 0):
msg = "Even"
else:
msg = "Odd"
print(msg)
For versions prior to 2.5, there's the trick:
[expression] and [on_true] or [on_false]
It can give wrong results when on_true
has a false boolean value.1
Although it does have the benefit of evaluating expressions left to right, which is clearer in my opinion.
Other answers correctly talk about the Python ternary operator. I would like to complement by mentioning a scenario for which the ternary operator is often used but for which there is a better idiom. This is the scenario of using a default value.
Suppose we want to use option_value with a default value if it is not set:
run_algorithm(option_value if option_value is not None else 10)
or, if option_value is never set to a falsy value (0, "", etc), simply
run_algorithm(option_value if option_value else 10)
However, in this case an ever better solution is simply to write
run_algorithm(option_value or 10)
Does Python have a ternary conditional operator?
Yes. From the grammar file:
test: or_test ['if' or_test 'else' test] | lambdef
The part of interest is:
or_test ['if' or_test 'else' test]
So, a ternary conditional operation is of the form:
expression1 if expression2 else expression3
expression3 will be lazily evaluated (that is, evaluated only if expression2 is false in a boolean context). And because of the recursive definition, you can chain them indefinitely (though it may considered bad style.)
expression1 if expression2 else expression3 if expression4 else expression5 # and so on
Note that every if must be followed with an else. People learning list comprehensions and generator expressions may find this to be a difficult lesson to learn - the following will not work, as Python expects a third expression for an else:
[expression1 if expression2 for element in iterable]
# ^-- need an else here
which raises a SyntaxError: invalid syntax.
So the above is either an incomplete piece of logic (perhaps the user expects a no-op in the false condition) or what may be intended is to use expression2 as a filter - notes that the following is legal Python:
[expression1 for element in iterable if expression2]
expression2 works as a filter for the list comprehension, and is not a ternary conditional operator.
You may find it somewhat painful to write the following:
expression1 if expression1 else expression2
expression1 will have to be evaluated twice with the above usage. It can limit redundancy if it is simply a local variable. However, a common and performant Pythonic idiom for this use-case is to use or's shortcutting behavior:
expression1 or expression2
which is equivalent in semantics. Note that some style-guides may limit this usage on the grounds of clarity - it does pack a lot of meaning into very little syntax.
For versions prior to 2.5, there's the trick:
[expression] and [on_true] or [on_false]
It can give wrong results when on_true
has a false boolean value.1
Although it does have the benefit of evaluating expressions left to right, which is clearer in my opinion.
Python has a ternary form for assignments; however there may be even a shorter form that people should be aware of.
It's very common to need to assign to a variable one value or another depending on a condition.
>>> li1 = None
>>> li2 = [1, 2, 3]
>>>
>>> if li1:
... a = li1
... else:
... a = li2
...
>>> a
[1, 2, 3]
^ This is the long form for doing such assignments.
Below is the ternary form. But this isn't most succinct way - see last example.
>>> a = li1 if li1 else li2
>>>
>>> a
[1, 2, 3]
>>>
With Python, you can simply use or for alternative assignments.
>>> a = li1 or li2
>>>
>>> a
[1, 2, 3]
>>>
The above works since li1 is None and the interp treats that as False in logic expressions. The interp then moves on and evaluates the second expression, which is not None and it's not an empty list - so it gets assigned to a.
This also works with empty lists. For instance, if you want to assign a whichever list has items.
>>> li1 = []
>>> li2 = [1, 2, 3]
>>>
>>> a = li1 or li2
>>>
>>> a
[1, 2, 3]
>>>
Knowing this, you can simply such assignments whenever you encounter them. This also works with strings and other iterables. You could assign a whichever string isn't empty.
>>> s1 = ''
>>> s2 = 'hello world'
>>>
>>> a = s1 or s2
>>>
>>> a
'hello world'
>>>
I always liked the C ternary syntax, but Python takes it a step further!
I understand that some may say this isn't a good stylistic choice because it relies on mechanics that aren't immediately apparent to all developers. I personally disagree with that viewpoint. Python is a syntax rich language with lots of idiomatic tricks that aren't immediately apparent to the dabler. But the more you learn and understand the mechanics of the underlying system, the more you appreciate it.
One of the alternatives to Python's conditional expression
"yes" if boolean else "no"
is the following:
{True:"yes", False:"no"}[boolean]
which has the following nice extension:
{True:"yes", False:"no", None:"maybe"}[boolean_or_none]
The shortest alternative remains:
("no", "yes")[boolean]
but there is no alternative to
yes() if boolean else no()
if you want to avoid the evaluation of yes() and no(), because in
(no(), yes())[boolean] # bad
both no() and yes() are evaluated.
if variable is defined and you want to check if it has value you can just a or b
def test(myvar=None):
# shorter than: print myvar if myvar else "no Input"
print myvar or "no Input"
test()
test([])
test(False)
test('hello')
test(['Hello'])
test(True)
will output
no Input
no Input
no Input
hello
['Hello']
True
Unfortunately, the
(falseValue, trueValue)[test]
solution doesn't have short-circuit behaviour; thus both falseValue and trueValue are evaluated regardless of the condition. This could be suboptimal or even buggy (i.e. both trueValue and falseValue could be methods and have side-effects).
One solution to this would be
(lambda: falseValue, lambda: trueValue)[test]()
(execution delayed until the winner is known ;)), but it introduces inconsistency between callable and non-callable objects. In addition, it doesn't solve the case when using properties.
And so the story goes - choosing between 3 mentioned solutions is a trade-off between having the short-circuit feature, using at least ?ython 2.5 (IMHO not a problem anymore) and not being prone to "trueValue-evaluates-to-false" errors.
Here I just try to show some important difference in ternary operator between a couple of programming languages.
Ternary Operator in Javascript
var a = true ? 1 : 0;
# 1
var b = false ? 1 : 0;
# 0
Ternary Operator in Ruby
a = true ? 1 : 0
# 1
b = false ? 1 : 0
# 0
Ternary operator in Scala
val a = true ? 1 | 0
# 1
val b = false ? 1 | 0
# 0
Ternary operator in R programming
a <- if (TRUE) 1 else 0
# 1
b <- if (FALSE) 1 else 0
# 0
Ternary operator in Python
a = 1 if True else 0
# 1
b = 1 if False else 0
# 0
An operator for a conditional expression in Python was added in 2006 as part of Python Enhancement Proposal 308. Its form differ from common ?: operator and it's:
<expression1> if <condition> else <expression2>
which is equivalent to:
if <condition>: <expression1> else: <expression2>
Here is an example:
result = x if a > b else y
Another syntax which can be used (compatible with versions before 2.5):
result = (lambda:y, lambda:x)[a > b]()
where operands are lazily evaluated.
Another way is by indexing a tuple (which isn't consistent with the conditional operator of most other languages):
result = (y, x)[a > b]
or explicitly constructed dictionary:
result = {True: x, False: y}[a > b]
Another (less reliable), but simpler method is to use and and or operators:
result = (a > b) and x or y
however this won't work if x would be False.
A possible workaround is to make x and y lists or tuples as in the following:
result = ((a > b) and [x] or [y])[0]
or:
result = ((a > b) and (x,) or (y,))[0]
If you're working with dictionaries, instead of using a ternary conditional, you can take advantage of get(key, default), for example:
shell = os.environ.get('SHELL', "/bin/sh")
Source: ?: in Python at Wikipedia
A neat way to chain multiple operators:
f = lambda x,y: 'greater' if x > y else 'less' if y > x else 'equal'
array = [(0,0),(0,1),(1,0),(1,1)]
for a in array:
x, y = a[0], a[1]
print(f(x,y))
# Output is:
# equal,
# less,
# greater,
# equal
Python has a ternary form for assignments; however there may be even a shorter form that people should be aware of.
It's very common to need to assign to a variable one value or another depending on a condition.
>>> li1 = None
>>> li2 = [1, 2, 3]
>>>
>>> if li1:
... a = li1
... else:
... a = li2
...
>>> a
[1, 2, 3]
^ This is the long form for doing such assignments.
Below is the ternary form. But this isn't most succinct way - see last example.
>>> a = li1 if li1 else li2
>>>
>>> a
[1, 2, 3]
>>>
With Python, you can simply use or for alternative assignments.
>>> a = li1 or li2
>>>
>>> a
[1, 2, 3]
>>>
The above works since li1 is None and the interp treats that as False in logic expressions. The interp then moves on and evaluates the second expression, which is not None and it's not an empty list - so it gets assigned to a.
This also works with empty lists. For instance, if you want to assign a whichever list has items.
>>> li1 = []
>>> li2 = [1, 2, 3]
>>>
>>> a = li1 or li2
>>>
>>> a
[1, 2, 3]
>>>
Knowing this, you can simply such assignments whenever you encounter them. This also works with strings and other iterables. You could assign a whichever string isn't empty.
>>> s1 = ''
>>> s2 = 'hello world'
>>>
>>> a = s1 or s2
>>>
>>> a
'hello world'
>>>
I always liked the C ternary syntax, but Python takes it a step further!
I understand that some may say this isn't a good stylistic choice because it relies on mechanics that aren't immediately apparent to all developers. I personally disagree with that viewpoint. Python is a syntax rich language with lots of idiomatic tricks that aren't immediately apparent to the dabler. But the more you learn and understand the mechanics of the underlying system, the more you appreciate it.
<expression 1> if <condition> else <expression 2>
a = 1
b = 2
1 if a > b else -1
# Output is -1
1 if a > b else -1 if a < b else 0
# Output is -1
if variable is defined and you want to check if it has value you can just a or b
def test(myvar=None):
# shorter than: print myvar if myvar else "no Input"
print myvar or "no Input"
test()
test([])
test(False)
test('hello')
test(['Hello'])
test(True)
will output
no Input
no Input
no Input
hello
['Hello']
True
For versions prior to 2.5, there's the trick:
[expression] and [on_true] or [on_false]
It can give wrong results when on_true
has a false boolean value.1
Although it does have the benefit of evaluating expressions left to right, which is clearer in my opinion.
The ternary operator is a way of writing conditional statements in Python. As the name ternary suggests, this Python operator consists of three operands.
Syntax: The three operands in a ternary operator include:
condition: A boolean expression that evaluates to either true or false.
true_val: A value to be assigned if the expression is evaluated to true.
false_val: A value to be assigned if the expression is evaluated to false.
var = true_val if condition else false_val
The variable var on the left-hand side of the = (assignment) operator will be assigned:
value1 if the booleanExpression evaluates to true.
value2 if the booleanExpression evaluates to false.
Example:
# USING TERNARY OPERATOR
to_check = 6
msg = "Even" if to_check%2 == 0 else "Odd"
print(msg)
# USING USUAL IF-ELSE
msg = ""
if(to_check%2 == 0):
msg = "Even"
else:
msg = "Odd"
print(msg)
I find cumbersome the default python syntax val = a if cond else b, so sometimes I do this:
iif = lambda (cond, a, b): a if cond else b
# so I can then use it like:
val = iif(cond, a, b)
Of course, it has the downside of always evaluating both sides (a and b), but the syntax it's way clearer to me
<expression 1> if <condition> else <expression 2>
a = 1
b = 2
1 if a > b else -1
# Output is -1
1 if a > b else -1 if a < b else 0
# Output is -1
Other answers correctly talk about the Python ternary operator. I would like to complement by mentioning a scenario for which the ternary operator is often used but for which there is a better idiom. This is the scenario of using a default value.
Suppose we want to use option_value with a default value if it is not set:
run_algorithm(option_value if option_value is not None else 10)
or, if option_value is never set to a falsy value (0, "", etc), simply
run_algorithm(option_value if option_value else 10)
However, in this case an ever better solution is simply to write
run_algorithm(option_value or 10)
Unfortunately, the
(falseValue, trueValue)[test]
solution doesn't have short-circuit behaviour; thus both falseValue and trueValue are evaluated regardless of the condition. This could be suboptimal or even buggy (i.e. both trueValue and falseValue could be methods and have side-effects).
One solution to this would be
(lambda: falseValue, lambda: trueValue)[test]()
(execution delayed until the winner is known ;)), but it introduces inconsistency between callable and non-callable objects. In addition, it doesn't solve the case when using properties.
And so the story goes - choosing between 3 mentioned solutions is a trade-off between having the short-circuit feature, using at least ?ython 2.5 (IMHO not a problem anymore) and not being prone to "trueValue-evaluates-to-false" errors.
One of the alternatives to Python's conditional expression
"yes" if boolean else "no"
is the following:
{True:"yes", False:"no"}[boolean]
which has the following nice extension:
{True:"yes", False:"no", None:"maybe"}[boolean_or_none]
The shortest alternative remains:
("no", "yes")[boolean]
but there is no alternative to
yes() if boolean else no()
if you want to avoid the evaluation of yes() and no(), because in
(no(), yes())[boolean] # bad
both no() and yes() are evaluated.
An operator for a conditional expression in Python was added in 2006 as part of Python Enhancement Proposal 308. Its form differ from common ?: operator and it's:
<expression1> if <condition> else <expression2>
which is equivalent to:
if <condition>: <expression1> else: <expression2>
Here is an example:
result = x if a > b else y
Another syntax which can be used (compatible with versions before 2.5):
result = (lambda:y, lambda:x)[a > b]()
where operands are lazily evaluated.
Another way is by indexing a tuple (which isn't consistent with the conditional operator of most other languages):
result = (y, x)[a > b]
or explicitly constructed dictionary:
result = {True: x, False: y}[a > b]
Another (less reliable), but simpler method is to use and and or operators:
result = (a > b) and x or y
however this won't work if x would be False.
A possible workaround is to make x and y lists or tuples as in the following:
result = ((a > b) and [x] or [y])[0]
or:
result = ((a > b) and (x,) or (y,))[0]
If you're working with dictionaries, instead of using a ternary conditional, you can take advantage of get(key, default), for example:
shell = os.environ.get('SHELL', "/bin/sh")
Source: ?: in Python at Wikipedia
From the documentation:
Conditional expressions (sometimes called a “ternary operator”) have the lowest priority of all Python operations.
The expression
x if C else yfirst evaluates the condition, C (not x); if C is true, x is evaluated and its value is returned; otherwise, y is evaluated and its value is returned.See PEP 308 for more details about conditional expressions.
New since version 2.5.
you can do this :-
[condition] and [expression_1] or [expression_2] ;Example:-
print(number%2 and "odd" or "even")This would print "odd" if the number is odd or "even" if the number is even.
Note :- 0 , None , False , emptylist , emptyString evaluates as False. And any data other than 0 evaluates to True.
if the condition [condition] becomes "True" then , expression_1 will be evaluated but not expression_2 . If we "and" something with 0 (zero) , the result will always to be fasle .So in the below statement ,
0 and exp
The expression exp won't be evaluated at all since "and" with 0 will always evaluate to zero and there is no need to evaluate the expression . This is how the compiler itself works , in all languages.
In
1 or exp
the expression exp won't be evaluated at all since "or" with 1 will always be 1. So it won't bother to evaluate the expression exp since the result will be 1 anyway . (compiler optimization methods).
But in case of
True and exp1 or exp2
The second expression exp2 won't be evaluated since True and exp1 would be True when exp1 isn't false .
Similarly in
False and exp1 or exp2
The expression exp1 won't be evaluated since False is equivalent to writing 0 and doing "and" with 0 would be 0 itself but after exp1 since "or" is used, it will evaluate the expression exp2 after "or" .
Note:- This kind of branching using "or" and "and" can only be used when the expression_1 doesn't have a Truth value of False (or 0 or None or emptylist [ ] or emptystring ' '.) since if expression_1 becomes False , then the expression_2 will be evaluated because of the presence "or" between exp_1 and exp_2.
In case you still want to make it work for all the cases regardless of what exp_1 and exp_2 truth values are, do this :-
[condition] and ([expression_1] or 1) or [expression_2] ;a if condition else b
Just memorize this pyramid if you have trouble remembering:
condition
if else
a b
Ternary conditional operator simply allows testing a condition in a single line replacing the multiline if-else making the code compact.
[on_true] if [expression] else [on_false]
# Program to demonstrate conditional operator
a, b = 10, 20
# Copy value of a in min if a < b else copy b
min = a if a < b else b
print(min) # Output: 10
# Python program to demonstrate ternary operator
a, b = 10, 20
# Use tuple for selecting an item
print( (b, a) [a < b] )
# Use Dictionary for selecting an item
print({True: a, False: b} [a < b])
# lamda is more efficient than above two methods
# because in lambda we are assure that
# only one expression will be evaluated unlike in
# tuple and Dictionary
print((lambda: b, lambda: a)[a < b]()) # in output you should see three 10
# Python program to demonstrate nested ternary operator
a, b = 10, 20
print ("Both a and b are equal" if a == b else "a is greater than b"
if a > b else "b is greater than a")
Above approach can be written as:
# Python program to demonstrate nested ternary operator
a, b = 10, 20
if a != b:
if a > b:
print("a is greater than b")
else:
print("b is greater than a")
else:
print("Both a and b are equal")
# Output: b is greater than a
YES, python have a ternary operator, here is the syntax and an example code to demonstrate the same :)
#[On true] if [expression] else[On false]
# if the expression evaluates to true then it will pass On true otherwise On false
a= input("Enter the First Number ")
b= input("Enter the Second Number ")
print("A is Bigger") if a>b else print("B is Bigger")
For Python 2.5 and newer there is a specific syntax:
[on_true] if [cond] else [on_false]
In older Pythons a ternary operator is not implemented but it's possible to simulate it.
cond and on_true or on_false
Though, there is a potential problem, which if cond evaluates to True and on_true evaluates to False then on_false is returned instead of on_true. If you want this behavior the method is OK, otherwise use this:
{True: on_true, False: on_false}[cond is True] # is True, not == True
which can be wrapped by:
def q(cond, on_true, on_false)
return {True: on_true, False: on_false}[cond is True]
and used this way:
q(cond, on_true, on_false)
It is compatible with all Python versions.
Simulating the python ternary operator.
For example
a, b, x, y = 1, 2, 'a greather than b', 'b greater than a'
result = (lambda:y, lambda:x)[a > b]()
output:
'b greater than a'
From the documentation:
Conditional expressions (sometimes called a “ternary operator”) have the lowest priority of all Python operations.
The expression
x if C else yfirst evaluates the condition, C (not x); if C is true, x is evaluated and its value is returned; otherwise, y is evaluated and its value is returned.See PEP 308 for more details about conditional expressions.
New since version 2.5.
a if condition else b
Just memorize this pyramid if you have trouble remembering:
condition
if else
a b
From the documentation:
Conditional expressions (sometimes called a “ternary operator”) have the lowest priority of all Python operations.
The expression
x if C else yfirst evaluates the condition, C (not x); if C is true, x is evaluated and its value is returned; otherwise, y is evaluated and its value is returned.See PEP 308 for more details about conditional expressions.
New since version 2.5.
Many programming languages derived from C usually have the following syntax of ternary conditional operator:
<condition> ? <expression1> : <expression2>
At first, the
PythonBenevolent Dictator For Life (I mean Guido van Rossum, of course) rejected it (as non-Pythonic style), since it's quite hard to understand for people not used toClanguage. Also, the colon sign:already has many uses inPython. After PEP 308 was approved,Pythonfinally received its own shortcut conditional expression (what we use now):
<expression1> if <condition> else <expression2>
So, firstly it evaluates the condition. If it returns True, expression1 will be evaluated to give the result, otherwise expression2 will be evaluated. Due to Lazy Evaluation mechanics – only one expression will be executed.
Here are some examples (conditions will be evaluated from left to right):
pressure = 10
print('High' if pressure < 20 else 'Critical')
# Result is 'High'
Ternary operators can be chained in series:
pressure = 5
print('Normal' if pressure < 10 else 'High' if pressure < 20 else 'Critical')
# Result is 'Normal'
The following one is the same as previous one:
pressure = 5
if pressure < 20:
if pressure < 10:
print('Normal')
else:
print('High')
else:
print('Critical')
# Result is 'Normal'
Hope this helps.
You might often find
cond and on_true or on_false
but this lead to problem when on_true == 0
>>> x = 0
>>> print x == 0 and 0 or 1
1
>>> x = 1
>>> print x == 0 and 0 or 1
1
where you would expect for a normal ternary operator this result
>>> x = 0
>>> print 0 if x == 0 else 1
0
>>> x = 1
>>> print 0 if x == 0 else 1
1
you can do this :-
[condition] and [expression_1] or [expression_2] ;Example:-
print(number%2 and "odd" or "even")This would print "odd" if the number is odd or "even" if the number is even.
Note :- 0 , None , False , emptylist , emptyString evaluates as False. And any data other than 0 evaluates to True.
if the condition [condition] becomes "True" then , expression_1 will be evaluated but not expression_2 . If we "and" something with 0 (zero) , the result will always to be fasle .So in the below statement ,
0 and exp
The expression exp won't be evaluated at all since "and" with 0 will always evaluate to zero and there is no need to evaluate the expression . This is how the compiler itself works , in all languages.
In
1 or exp
the expression exp won't be evaluated at all since "or" with 1 will always be 1. So it won't bother to evaluate the expression exp since the result will be 1 anyway . (compiler optimization methods).
But in case of
True and exp1 or exp2
The second expression exp2 won't be evaluated since True and exp1 would be True when exp1 isn't false .
Similarly in
False and exp1 or exp2
The expression exp1 won't be evaluated since False is equivalent to writing 0 and doing "and" with 0 would be 0 itself but after exp1 since "or" is used, it will evaluate the expression exp2 after "or" .
Note:- This kind of branching using "or" and "and" can only be used when the expression_1 doesn't have a Truth value of False (or 0 or None or emptylist [ ] or emptystring ' '.) since if expression_1 becomes False , then the expression_2 will be evaluated because of the presence "or" between exp_1 and exp_2.
In case you still want to make it work for all the cases regardless of what exp_1 and exp_2 truth values are, do this :-
[condition] and ([expression_1] or 1) or [expression_2] ;For versions prior to 2.5, there's the trick:
[expression] and [on_true] or [on_false]
It can give wrong results when on_true
has a false boolean value.1
Although it does have the benefit of evaluating expressions left to right, which is clearer in my opinion.
As already answered, yes there is a ternary operator in python:
<expression 1> if <condition> else <expression 2>
Additional information:
If <expression 1> is the condition you can use Short-cirquit evaluation:
a = True
b = False
# Instead of this:
x = a if a else b
# You could use Short-cirquit evaluation:
x = a or b
PS: Of course, a Short-cirquit evaluation is not a ternary operator but often the ternary is used in cases where the short circuit would be enough.
A neat way to chain multiple operators:
f = lambda x,y: 'greater' if x > y else 'less' if y > x else 'equal'
array = [(0,0),(0,1),(1,0),(1,1)]
for a in array:
x, y = a[0], a[1]
print(f(x,y))
# Output is:
# equal,
# less,
# greater,
# equal
As already answered, yes there is a ternary operator in python:
<expression 1> if <condition> else <expression 2>
Additional information:
If <expression 1> is the condition you can use Short-cirquit evaluation:
a = True
b = False
# Instead of this:
x = a if a else b
# You could use Short-cirquit evaluation:
x = a or b
PS: Of course, a Short-cirquit evaluation is not a ternary operator but often the ternary is used in cases where the short circuit would be enough.
Here I just try to show some important difference in ternary operator between a couple of programming languages.
Ternary Operator in Javascript
var a = true ? 1 : 0;
# 1
var b = false ? 1 : 0;
# 0
Ternary Operator in Ruby
a = true ? 1 : 0
# 1
b = false ? 1 : 0
# 0
Ternary operator in Scala
val a = true ? 1 | 0
# 1
val b = false ? 1 | 0
# 0
Ternary operator in R programming
a <- if (TRUE) 1 else 0
# 1
b <- if (FALSE) 1 else 0
# 0
Ternary operator in Python
a = 1 if True else 0
# 1
b = 1 if False else 0
# 0
is_spacial=True if gender = "Female" else (True if age >= 65 else False)
**
it can be nested as your need. best of luck
**
YES, python have a ternary operator, here is the syntax and an example code to demonstrate the same :)
#[On true] if [expression] else[On false]
# if the expression evaluates to true then it will pass On true otherwise On false
a= input("Enter the First Number ")
b= input("Enter the Second Number ")
print("A is Bigger") if a>b else print("B is Bigger")
Many programming languages derived from C usually have the following syntax of ternary conditional operator:
<condition> ? <expression1> : <expression2>
At first, the
PythonBenevolent Dictator For Life (I mean Guido van Rossum, of course) rejected it (as non-Pythonic style), since it's quite hard to understand for people not used toClanguage. Also, the colon sign:already has many uses inPython. After PEP 308 was approved,Pythonfinally received its own shortcut conditional expression (what we use now):
<expression1> if <condition> else <expression2>
So, firstly it evaluates the condition. If it returns True, expression1 will be evaluated to give the result, otherwise expression2 will be evaluated. Due to Lazy Evaluation mechanics – only one expression will be executed.
Here are some examples (conditions will be evaluated from left to right):
pressure = 10
print('High' if pressure < 20 else 'Critical')
# Result is 'High'
Ternary operators can be chained in series:
pressure = 5
print('Normal' if pressure < 10 else 'High' if pressure < 20 else 'Critical')
# Result is 'Normal'
The following one is the same as previous one:
pressure = 5
if pressure < 20:
if pressure < 10:
print('Normal')
else:
print('High')
else:
print('Critical')
# Result is 'Normal'
Hope this helps.
From the documentation:
Conditional expressions (sometimes called a “ternary operator”) have the lowest priority of all Python operations.
The expression
x if C else yfirst evaluates the condition, C (not x); if C is true, x is evaluated and its value is returned; otherwise, y is evaluated and its value is returned.See PEP 308 for more details about conditional expressions.
New since version 2.5.
Source: Stackoverflow.com