What exactly does do in python

Question

I need to know what    does in Python  It s that simple  I also would appreciate links to definitions of other shorthand tools in Python

User · Answer

Remember when you used to sum  for example 2  amp  3  in your old calculator and every time you hit the   you see 3 added to the total  the    does similar job  Example    gt  gt  gt  orange   2  gt  gt  gt  orange    3  gt  gt  gt  print orange  5  gt  gt  gt  orange   3  gt  gt  gt  print orange  8

User · Answer

According to the documentation  x    y is equivalent to x   operator iadd x  y   Another way to put it is to say that z   operator iadd x  y  is equivalent to the compound statement z   x  z    y   So x    3 is the same as x   x   3  x   2  x    3  print x   will output 5  Notice that there s also   amp        lt  lt                    gt  gt   -

User · Answer

It is not mere a syntactic sugar     Try this  x                        empty list x     quot something quot          iterates over the string and appends to list print x                    s    o    m    e    t    h    i    n    g    versus x                        empty list x   x    quot something quot       TypeError  can only concatenate list  not  quot str quot   to list  The    operator invokes the   iadd     list method  while   one invokes the   add     one  They do different things with lists

User · Answer

In Python     is sugar coating for the   iadd   special method  or   add   or   radd   if   iadd   isn t present   The   iadd   method of a class can do anything it wants   The list object implements it and uses it to iterate over an iterable object appending each element to itself in the same way that the list s extend method does   Here s a simple custom class that implements the   iadd   special method  You initialize the object with an int  then can use the    operator to add a number   I ve added a print statement in   iadd   to show that it gets called   Also    iadd   is expected to return an object  so I returned the addition of itself plus the other number which makes sense in this case    gt  gt  gt  class Adder object           def   init   self  num 0               self num   num          def   iadd   self  other               print  in   iadd     other             self num   self num   other             return self num   gt  gt  gt  a   Adder 2   gt  gt  gt  a    3 in   iadd   3  gt  gt  gt  a 5   Hope this helps

User · Answer

x    5 is not exactly the same as saying x   x   5 in Python  Note here  In  1   x    2  3  4      In  2   y   x     In  3   x    7  8  9     In  4   x Out 4    2  3  4  7  8  9      In  5   y Out 5    2  3  4  7  8  9      In  6   x     44  55      In  7   x Out 7    2  3  4  7  8  9  44  55      In  8   y Out 8    2  3  4  7  8  9  44  55      In  9   x   x    33  22      In  10   x Out 10    2  3  4  7  8  9  44  55  33  22      In  11   y Out 11    2  3  4  7  8  9  44  55   See for reference  Why does    behave unexpectedly on lists

User · Answer

adds a number to a variable  changing the variable itself in the process  whereas   would not   Similar to this  there are the following that also modifies the variable    -   subtracts a value from variable  setting the variable to the result     multiplies the variable and a value  making the outcome the variable     divides the variable by the value  making the outcome the variable     performs modulus on the variable  with the variable then being set to the result of it   There may be others  I am not a Python programmer

User · Answer

Notionally a    b  adds  b to a storing the result in a  This simplistic description would describe the    operator in many languages   However the simplistic description raises a couple of questions    What exactly do we mean by  adding   What exactly do we mean by  storing the result in a   python variables don t store values directly they store references to objects    In python the answers to both of these questions depend on the data type of a     So what exactly does  adding  mean    For numbers it means numeric addition  For lists  tuples  strings etc it means concatenation    Note that for lists    is more flexible than    the   operator on a list requires another list  but the    operator will accept any iterable     So what does  storing the value in a  mean    If the object is mutable then it is encouraged  but not required  to perform the modification in-place  So a points to the same object it did before but that object now has different content   If the object is immutable then it obviously can t perform the modification in-place  Some mutable objects may also not have an implementation of an in-place  add  operation   In this case the variable  a  will be updated to point to a new object containing the result of an addition operation   Technically this is implemented by looking for   IADD   first  if that is not implemented then   ADD   is tried and finally   RADD       Care is required when using    in python on variables where we are not certain of the exact type and in particular where we are not certain if the type is mutable or not  For example consider the following code   def dostuff a       b   a     a     3 4      print repr a      repr b    dostuff  1 2   dostuff  1 2     When we invoke dostuff with a tuple then the tuple is copied as part of the    operation and so b is unaffected  However when we invoke it with a list the list is modified in place  so both a and b are affected    In python 3  similar behaviour is observed with the  bytes  and  bytearray  types      Finally note that reassignment happens even if the object is not replaced  This doesn t matter much if the left hand side is simply a variable but it can cause confusing behaviour when you have an immutable collection referring to mutable collections for example    a     1 2   3 4   a 0      5    In this case  5  will successfully be added to the list referred to by a 0  but then afterwards an exception will be raised when the code tries and fails to reassign a 0

User · Answer

As others also said  the    operator is a shortcut  An example   var   1  var   var   1   var   2   It could also be written like so   var   1  var    1   var   2   So instead of writing the first example  you can just write the second one  which would work just fine

User · Answer

adds another value with the variable s value and assigns the new value to the variable    gt  gt  gt  x   3  gt  gt  gt  x    2  gt  gt  gt  print x 5   -          does similar for subtraction  multiplication and division

User · Answer

is just a shortcut for writing   number   4 number   number   1   So instead you would write  numbers   4 numbers    1   Both ways are correct but example two helps you write a little less code

User · Answer

I m seeing a lot of answers that don t bring up using    with multiple integers   One example   x -  1   3   This would be similar to   x   x -  1   3    and not   x    x - 1    3

User · Answer

It adds the right operand to the left   x    2 means x   x   2  It can also add elements to a list -- see this SO thread

User · Answer

The short answer is    can be translated as  add whatever is to the right of the    to the variable on the left of the       Ex  If you have a   10 then a    5 would be   a   a   5  So   a  now equal to 15

User · Answer

Note x    y is not the same as x   x   y in some situations where an additional operator is included because of the operator precedence combined with the fact that the right hand side is always evaluated first  e g    gt  gt  gt  x   2  gt  gt  gt  x    2 and 1  gt  gt  gt  x 3   gt  gt  gt  x   2  gt  gt  gt  x   x   2 and 1  gt  gt  gt  x 1   Note the first case expand to    gt  gt  gt  x   2  gt  gt  gt  x   x    2 and 1   gt  gt  gt  x 3   You are more likely to encounter this in the  real world  with other operators  e g   x    2   1    x   x    2   1     x   x   2   1

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