What is the purpose of the return statement

Question

What is the simple basic explanation of what the return statement is  how to use it in Python   And what is the difference between it and the print statement

User · Answer

I think a really simple answer might be useful here:

return makes the value (a variable, often) available for use by the caller (for example, to be stored by a function that the function using return is within). Without return, your value or variable wouldn't be available for the caller to store/re-use.

print prints to the screen, but does not make the value or variable available for use by the caller.

(Fully admitting that the more thorough answers are more accurate.)

User · Answer

Think of the print statement as causing a side-effect  it makes your function write some text out to the user  but it can t be used by another function   I ll attempt to explain this better with some examples  and a couple definitions from Wikipedia   Here is the definition of a function from Wikipedia  A function  in mathematics  associates one quantity  the argument of the function  also known as the input  with another quantity  the value of the function  also known as the output    Think about that for a second  What does it mean when you say the function has a value   What it means is that you can actually substitute the value of a function with a normal value   Assuming the two values are the same type of value   Why would you want that you ask   What about other functions that may accept the same type of value as an input   def square n       return n   n  def add one n       return n   1  print square 12     square 12  is the same as writing 144  print add one square 12   print add one 144   These both have the same output   There is a fancy mathematical term for functions that only depend on their inputs to produce their outputs  Referential Transparency  Again  a definition from Wikipedia   Referential transparency and referential opaqueness are properties of parts of computer programs  An expression is said to be referentially transparent if it can be replaced with its value without changing the behavior of a program  It might be a bit hard to grasp what this means if you re just new to programming  but I think you will get it after some experimentation  In general though  you can do things like print in a function  and you can also have a return statement at the end   Just remember that when you use return you are basically saying  A call to this function is the same as writing the value that gets returned   Python will actually insert a return value for you if you decline to put in your own  it s called  None   and it s a special type that simply means nothing  or null

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Difference between  return  and  print  can also be found in the following example   RETURN   def bigger a  b       if a  gt  b          return a     elif a  lt b          return b     else          return a   The above code will give correct results for all inputs   PRINT   def bigger a  b       if a  gt  b          print a     elif a  lt b          print b     else          print a   NOTE  This will fail for many test cases   ERROR   ----     FAILURE  Test case input  3  8                 Expected result  8     FAILURE  Test case input  4  3                 Expected result  4     FAILURE  Test case input  3  3                 Expected result  3       You passed 0 out of 3 test cases

User · Answer

I think the dictionary is your best reference here  Return and Print  In short   return gives something back or replies to the caller of the function while print produces text

User · Answer

This answer goes over some of the cases that have not been discussed above  The return statement allows you to terminate the execution of a function before you reach the end  This causes the flow of execution to immediately return to the caller    In line number 4   def ret n       if n  gt  9           temp    two digits           return temp      Line 4             else           temp    one digit           return temp      Line 8     print  return statement   ret 10    After the conditional statement gets executed the ret   function gets terminated due to return temp  line 4   Thus the print  return statement   does not get executed   Output    two digits      This code that appears after the conditional statements  or the place the flow of control cannot reach  is the dead code   Returning Values In lines number 4 and 8  the return statement is being used to return the value of a temporary variable after the condition has been executed   To bring out the difference between print and return   def ret n       if n  gt  9          print  two digits           return  two digits                 else           print  one digit           return  one digit          ret 25    Output    two digits  two digits

User · Answer

return should be used for recursive functions methods or you want to use the returned value for later applications in your algorithm   print should be used when you want to display a meaningful and desired output to the user and you don t want to clutter the screen with intermediate results that the user is not interested in  although they are helpful for debugging your code   The following code shows how to use return and print properly   def fact x       if x  lt  2          return 1     return x   fact x - 1   print fact 5     This explanation is true for all of the programming languages not just python

User · Answer

return is part of a function definition  while print outputs text to the standard output  usually the console    A function is a procedure accepting parameters and returning a value  return is for the latter  while the former is done with def   Example   def timestwo x       return x 2

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In python  we start defining a function with  def  and generally  but not necessarily  end the function with  return    A function of variable x is denoted as f x   What this function does  Suppose  this function adds 2 to x  So  f x  x 2  Now  the code of this function will be   def A function  x       return x   2   After defining the function  you can use that for any variable and get result  Such as   print A function  2   gt  gt  gt  4   We could just write the code slightly differently  such as   def A function  x       y   x   2     return y print A function  2    That would also give  4    Now  we can even use this code   def A function  x       x   x   2     return x print A function  2    That would also give 4  See  that the  x  beside return actually means  x 2   not x of  A function x     I guess from this simple example  you would understand the meaning of return command

User · Answer

Here is my understanding   hope it will help someone and it s correct     def count number of x       count   0     for item in x          if item     what you look for           count   count   1     return count   So this simple piece of code counts number of occurrences of something  The placement of return is significant  It tells your program where do you need the value  So when you print  you send output to the screen  When you return you tell the value to go somewhere  In this case you can see that count   0 is indented with return - we want the value  count   1  to replace 0   If you try to follow logic of the code when you indent the return command further the output will always be 1  because we would never tell the initial count to change  I hope I got it right   Oh  and return is always inside a function

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Best thing about return function is you can return a value from function but you can do same with print so whats the difference   Basically return not about just returning it gives output in object form so that we can save that return value from function to any variable but we can t do with print because its same like stdout cout in C Programming  Follow below code for better understanding CODE def add a  b       print  quot ADDING  d    d quot     a  b      return a   b  def subtract a  b       print  quot SUBTRACTING  d -  d quot     a  b      return a - b  def multiply a  b       print  quot MULTIPLYING  d    d quot     a  b      return a   b  def divide a  b       print  quot DIVIDING  d    d quot     a  b      return a   b   print  quot Let s do some math with just functions  quot   age   add 30  5  height   subtract 78  4  weight   multiply 90  2  iq   divide 100  2   print  quot Age   d  Height   d  Weight   d  IQ   d quot     age  height  weight  iq      A puzzle for the extra credit  type it in anyway  print  quot Here is a puzzle  quot   what   add age  subtract height  multiply weight  divide iq  2      print  quot That becomes   quot   what   quot Can you do it by hand  quot   We are now doing our own math functions for add  subtract  multiply  and divide  The important thing to notice is the last line where we say return a   b  in add   What this does is the following   Our function is called with two arguments  a and b  We print out what our function is doing  in this case  quot ADDING  quot  Then we tell Python to do something kind of backward  we return the addition of a   b  You might say this as   quot I add a and b then return them  quot  Python adds the two numbers  Then when the function ends  any line that runs it will be able to assign this a   b result to a variable

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return means   output this value from this function    print means   send this value to  generally  stdout   In the Python REPL  a function return will be output to the screen by default  this isn t quite the same as print    This is an example of print    gt  gt  gt  n    foo nbar   just assigning a variable  No output  gt  gt  gt  n  the value is output  but it is in a  raw form   foo nbar   gt  gt  gt  print n  the  n is now a newline foo bar  gt  gt  gt    This is an example of return    gt  gt  gt  def getN           return  foo nbar       gt  gt  gt  getN    When this isn t assigned to something  it is just output  foo nbar   gt  gt  gt  n   getN     assigning a variable to the return value  No output  gt  gt  gt  n  the value is output  but it is in a  raw form   foo nbar   gt  gt  gt  print n  the  n is now a newline foo bar  gt  gt  gt

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Just to add to  Nathan Hughes s excellent answer   The return statement can be used as a kind of control flow  By putting one  or more  return statements in the middle of a function  we can say   stop executing this function  We ve either got what we wanted or something s gone wrong    Here s an example    gt  gt  gt  def make 3 characters long some string           if len some string     3              return False         if str some string     some string              return  Not a string           if len some string   lt  3              return    join some string  x     3          return some string   3        gt  gt  gt  threechars   make 3 characters long  xyz        gt  gt  gt  if threechars          print threechars     else          print  threechars is already 3 characters long        threechars is already 3 characters long    See the Code Style section of the Python Guide for more advice on this way of using return

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The print   function writes  i e    prints   a string in the console  The return statement causes your function to exit and hand back a value to its caller  The point of functions in general is to take in inputs and return something  The return statement is used when a function is ready to return a value to its caller    For example  here s a function utilizing both print   and return   def foo        print  hello from inside of foo       return 1   Now you can run code that calls foo  like so   if   name         main         print  going to call foo       x   foo       print  called foo       print  foo returned     str x     If you run this as a script  e g  a  py file  as opposed to in the Python interpreter  you will get the following output   going to call foo hello from inside foo called foo    foo returned 1   I hope this makes it clearer  The interpreter writes return values to the console so I can see why somebody could be confused   Here s another example from the interpreter that demonstrates that    gt  gt  gt  def foo            print  hello from within foo           return 1      gt  gt  gt  foo   hello from within foo 1  gt  gt  gt  def bar          return 10   foo        gt  gt  gt  bar   hello from within foo 10   You can see that when foo   is called from bar    1 isn t written to the console  Instead it is used to calculate the value returned from bar       print   is a function that causes a side effect  it writes a string in the console   but execution resumes with the next statement  return causes the function to stop executing and hand a value back to whatever called it

[python] What is the purpose of the return statement?

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