Putting an if-elif-else statement on one line

Question

I have read the links below  but it doesn t address my question  Does Python have a ternary conditional operator   the question is about  condensing if-else statement to one line   Is there an easier way of writing an if-elif-else statement so it fits on one line  For example   if expression1     statement1 elif expression2     statement2 else     statement3   Or a real-world example   if i  gt  100      x   2 elif i  lt  100      x   1 else      x   0   I just feel if the example above could be written the following way  it could look like more concise   x 2 if i gt 100 elif i lt 100 1 else 0  WRONG

User · Answer

You can optionally actually use the get method of a dict   x    i lt 100  -1  -10 lt  i lt  10  0  i gt 100  1  get True  2    You don t need the get method if one of the keys is guaranteed to evaluate to True   x    i lt 0  -1  i  0  0  i gt 0  1  True    At most one of the keys should ideally evaluate to True  If more than one key evaluates to True  the results could seem unpredictable

User · Answer

Despite some other answers  YES it IS possible   if expression1     statement1 elif expression2     statement2 else     statement3   translates to the following one liner   statement1 if expression1 else  statement2 if expression2 else statement3    in fact you can nest those till infinity  Enjoy

User · Answer

Just nest another if clause in the else statement   But that doesn t make it look any prettier    gt  gt  gt  x 5  gt  gt  gt  x if x gt 0 else   zero  if x  0 else  invalid value   5  gt  gt  gt  x   0  gt  gt  gt  x if x gt 0 else   zero  if x  0 else  invalid value    zero   gt  gt  gt  x   -1  gt  gt  gt  x if x gt 0 else   zero  if x  0 else  invalid value    invalid value

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You can use nested ternary if statements     if-else ternary construct country code    USA  is USA   True if country code     USA  else False print  is USA    is USA     if-elif-else ternary construct   Create function to avoid repeating code  def get age category name age       age category name    Young  if age  lt   40 else   Middle Aged  if age  gt  40 and age  lt   65 else  Senior       return age category name  print get age category name 25   print get age category name 50   print get age category name 75

User · Answer

The ternary operator is the best way to a concise expression  The syntax is variable   value 1 if condition else value 2  So  for your example  you must apply the ternary operator twice   i   23   set any value for i x   2 if i  gt  100 else 1 if i  lt  100 else 0

User · Answer

No  it s not possible  at least not with arbitrary statements   nor is it desirable  Fitting everything on one line would most likely violate PEP-8 where it is mandated that lines should not exceed 80 characters in length   It s also against the Zen of Python   Readability counts    Type import this at the Python prompt to read the whole thing    You can use a ternary expression in Python  but only for expressions  not for statements    gt  gt  gt  a    Hello  if foo   else  Goodbye    Edit   Your revised question now shows that the three statements are identical except for the value being assigned  In that case  a chained ternary operator does work  but I still think that it s less readable    gt  gt  gt  i 100  gt  gt  gt  a   1 if i lt 100 else 2 if i gt 100 else 0  gt  gt  gt  a 0  gt  gt  gt  i 101  gt  gt  gt  a   1 if i lt 100 else 2 if i gt 100 else 0  gt  gt  gt  a 2  gt  gt  gt  i 99  gt  gt  gt  a   1 if i lt 100 else 2 if i gt 100 else 0  gt  gt  gt  a 1

User · Answer

People have already mentioned ternary expressions  Sometimes with a simple conditional assignment as your example  it is possible to use a mathematical expression to perform the conditional assignment  This may not make your code very readable  but it does get it on one fairly short line  Your example could be written like this   x   2  i gt 100    1  i lt 100    The comparisons would be True or False  and when multiplying with numbers would then be either 1 or 0  One could use a   instead of an   in the middle

User · Answer

There s an alternative that s quite unreadable in my opinion but I ll share anyway just as a curiosity   x    i gt 100 and 2  or  i lt 100 and 1  or 0   More info here  https   docs python org 3 library stdtypes html boolean-operations-and-or-not

User · Answer

It also depends on the nature of your expressions  The general advice on the other answers of  quot not doing it quot  is quite valid for generic statements and generic expressions  But if all you need is a  quot dispatch quot  table  like  calling a different function depending on the value of a given option  you can put the functions to call inside a dictionary  Something like  def save            def edit           options     quot save quot   save   quot edit quot   edit   quot remove quot   lambda    quot Not Implemented quot    option   get input   result   options option     Instead of an if-else  if option   quot save quot       save

User · Answer

if i  gt  100      x   2 elif i  lt  100      x   1 else      x   0   If you want to use the above-mentioned code in one line  you can use the following     x   2 if i  gt  100 else 1 if i  lt  100 else 0   On doing so  x will be assigned 2 if i   100  1 if i  lt  100 and 0 if i   100

User · Answer

If you only need different expressions for different cases then this may work for you   expr1 if condition1 else expr2 if condition2 else expr   For example   a    neg  if b lt 0 else  pos  if b gt 0 else  zero

User · Answer

MESSAGELENGHT   39  quot A normal function call using if elif and else  quot  if MESSAGELENGHT    16      Datapacket    quot word quot  elif MESSAGELENGHT    8       Datapacket    byte  else       Datapacket    bit    similarly for a oneliner expresion        Datapacket    quot word quot  if MESSAGELENGHT    16 else  byte  if MESSAGELENGHT    8 else  bit  print Datapacket   Thanks

[python] Putting an if-elif-else statement on one line?

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