Understanding repr function in Python

Question

repr    evaluatable string representation of an object  can  eval    it  meaning it is a string representation that evaluates to a Python object   In other words    gt  gt  gt  x    foo   gt  gt  gt  repr x    foo     Questions    Why do I get the double quotes  when I do repr x    I don t get them when I do str x   Why do I get  foo  when I do eval   foo    and not x which is the object

User · Answer

The feedback you get on the interactive interpreter uses repr too. When you type in an expression (let it be expr), the interpreter basically does result = expr; if result is not None: print repr(result). So the second line in your example is formatting the string foo into the representation you want ('foo'). And then the interpreter creates the representation of that, leaving you with double quotes.

Why when I combine %r with double-quote and single quote escapes and print them out, it prints it the way I'd write it in my .py file but not the way I'd like to see it?

I'm not sure what you're asking here. The text single ' and double " quotes, when run through repr, includes escapes for one kind of quote. Of course it does, otherwise it wouldn't be a valid string literal by Python rules. That's precisely what you asked for by calling repr.

Also note that the eval(repr(x)) == x analogy isn't meant literal. It's an approximation and holds true for most (all?) built-in types, but the main thing is that you get a fairly good idea of the type and logical "value" from looking the the repr output.

User · Answer

When you say  foo    bar  baz foo    you are not passing foo to the baz function   foo is just a name used to represent a value  in this case  bar   and that value is passed to the baz function

User · Answer

1  The result of repr  foo   is the string  foo   In your Python shell  the result of the expression is expressed as a representation too  so you re essentially seeing repr repr  foo      2  eval calculates the result of an expression  The result is always a value  such as a number  a string  or an object   Multiple variables can refer to the same value  as in   x    foo  y   x   x and y now refer to the same value   3  I have no idea what you meant here  Can you post an example  and what you d like to see

User · Answer

gt  gt  gt  x    foo   gt  gt  gt  x  foo    So the name x is attached to  foo  string  When you call for example repr x  the interpreter puts  foo  instead of x and then calls repr  foo      gt  gt  gt  repr x    foo    gt  gt  gt  x   repr       foo     repr actually calls a magic method   repr   of x  which gives the string containing the representation of the value  foo  assigned to x  So it returns  foo  inside the string    resulting in   foo    The idea of repr is to give a string which contains a series of symbols which we can type in the interpreter and get the same value which was sent as an argument to repr    gt  gt  gt  eval   foo     foo    When we call eval   foo     it s the same as we type  foo  in the interpreter  It s as we directly type the contents of the outer string    in the interpreter    gt  gt  gt  eval  foo    Traceback  most recent call last     File   lt pyshell 5 gt    line 1  in  lt module gt      eval  foo     File   lt string gt    line 1  in  lt module gt  NameError  name  foo  is not defined   If we call eval  foo    it s the same as we type foo in the interpreter  But there is no foo variable available and an exception is raised    gt  gt  gt  str x   foo   gt  gt  gt  x   str      foo   gt  gt  gt     str is just the string representation of the object  remember  x variable refers to  foo    so this function returns string    gt  gt  gt  str 5   5    String representation of integer 5 is  5     gt  gt  gt  str  foo    foo    And string representation of string  foo  is the same string  foo

User · Answer

str   is used for creating output for end user while repr   is used for debuggin development And it s represent the official of object   Example    gt  gt  gt  import datetime  gt  gt  gt  today   datetime datetime now    gt  gt  gt  str today   2018-04-08 18 00 15 178404   gt  gt  gt  repr today   datetime datetime 2018  4  8  18  3  21  167886     From output we see that repr   shows the official representation of date object

[python] Understanding repr( ) function in Python

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