Denys Fisher, of Spirograph fame, using a computer late 1976, early 1977. Making it less human-readable? Transcript Discussion In this lesson, you'll see how to use a second dunder method that controls how ojects are converted to strings, the .__repr__ (): class Car: def __init__(self, color, mileage): self.color = color self.mileage = mileage def __repr__(self): return '__repr__ for Car' def __str__(self): return '__str__ for Car' Ask Question Asked 14 years, 3 months ago Modified 5 months ago Viewed 115k times 139 In Java, if I call List.toString (), it will automatically call the toString () method on each object inside the List. Hope this help you build concrete grounds to explore more answers. Python objects have two different string representations, namely _ _ str _ _ and _ _ repr _ _, in some cases these can return the same value, but there is an important difference between the two. What would a potion that increases resistance to damage actually do to the body? __str__ (self) Why is __repr__ called in the code below? How does its .__str__() and .__repr__() function react, and what result do we get from it? Specifically, the strings in a container would find it way too easy to disturb its string representation. If you don't define a __str__ () method for a class, then the built-in object implementation calls the __repr__ () method instead. In the given example, we are using the str() function on a string and floating values in Python. [Python-ideas] Enum and the Standard Library (and __str__ and __repr__) Ethan Furman. [/python] You can see in the example above that the outputs for the first example (x) are identical, but when you use __repr__ and __str__ with a string rather than a number, there's a noticeable difference. This comprehensive guide seeks to illuminate the distinctive functionalities of these two methods, their . Understanding the repr function, or __repr__ method is essential for understanding __str__, as both of them are used in conjunction. Pros and cons of "anything-can-happen" UB versus allowing particular deviations from sequential progran execution. What is the difference between these codes, and what does the repr do? Now, those implementations are just dummy implementations that are going to tell us whats going on behind the scenes. Where to start with a large crack the lock puzzle like this? Dan Bader __str__ or str() is used for creating output that is human-readable are must be for end-users. We have introduced a class named Animal and we have built an object a for it. For many objects, __repr__ and __str__ are the same function. __repr__ is more for developers while __str__ is for end users. The following example shows how it works. And now, if we do my_car and just inspect that, we can see here that its actually called .__repr__() for the Car. Python __repr__ () magic method Syntax Syntax: object.__repr__ () How to input multiple values from user in one line in Python. @SolomonUcko yes in Python 3, that would seem to be the case - I've been hunting down the source code where this is implemented and I'll update my answer with that information when I get it together. Includes 82 Lessons Course Learn the basics of Python 3, one of the most powerful, versatile, and in-demand programming languages today. Similarly, we can get the string representation of an object using the repr() function. How do I write the reference mark symbol in TeX? We could also go through the .format() example againyou can see it called the .__str__() function. The default implementation defined by the built-in type object calls object.__repr__(). And so some people actually recommend that the result of your .__repr__() should be something like this, that would actually be valid Python and that you could just run again and would recreate the same object. And another way to force this is to call the built-in repr() function, and then thats going to do the right thing and call the correct .__repr__() implementation for this. The __repr__ method is present either when doing something like repr(your_object), or when a programmer might actually just type the object directly into the interpreter. goal is to return a printable string. If the class definition does not contain the __str__ method, then __repr__ method is invoked by python interpreter. For this reason, if I have a simple enough __str__, I generally just try to get the best of both worlds with something like: When print() is called on the result of decimal.Decimal(23) / decimal.Decimal("1.05") the raw number is printed; this output is in string form which can be achieved with __str__(). From the above output, we can see if we print a string using the repr() function then it prints with a pair of quotes and if we calculate a value we get a more precise value than the str() function. In Python __str__ is meant to return the object's human-friendly representation, while __repr__ should return a valid python expression that can be . The solution here is adding the .__str__ () and .__repr__ () "dunder" methods (some call them "magic methods") to your class. Return a string containing a nicely printable Now, of course, the big question is, Okay, so now we have these twowhats actually the difference between them, or whats the different use cases where you would use them?. Here, you can observe that we can obtain an integer object from a string representation of the integer obtained using the __str__() method and the __repr__() method. What is the difference between __str__ and __repr__? The goal here really is to be as explicit as possible about what this object, I guess, more meant for internal use and something that would make things easier. When we just inspected the object, __repr__was called while when we used the print method, __str__ was called. That is why the Multiplication implemented in c++ with constant time, Passport "Issued in" vs. "Issuing Country" & "Issuing Authority", Adding salt pellets direct to home water tank. If you want the above behavior when youre printing a list, just. Let's look at how useful it can be, using the Python shell and datetime objects. The goal of __repr__ is to be unambiguous, Let me come right out and say it I do not believe in debuggers. Have a look at this output that was returned by the __repr__() method in the previous section: Pythonic OOP String Conversion: .__repr__() vs .__str__() Unless you are logging EVERYTHING you can't get that. Lets take the same Animal class to ease things up. Both str() and repr() have the same basic job: their goal is to return a string representation of a Python object. Same mesh but different objects with separate UV maps? The __str__ method returns a string representation of an object that is human-readable while the __repr__ method returns a string representation of an object that is machine-readable. Starting the Prompt Design Site: A New Home in our Stack Exchange Neighborhood. Very similar, and both of these methods contain the same information, but the __str__ is a bit more human friendly. What is the reason for list.__str__ using __repr__ of its elements? From Fluent Python book, by Ramalho, Luciano. The __str__() method returns the objects string representation. itself. 1 But when I do the following: uno.neighbours.append ( [ [due, 4], [tri, 5]]) and then print uno.neighbours I get [ [ [<__main__.Node instance at 0x00000000023A6C48>, 4], [<__main__.Node instance at 0x00000000023A6D08>, 5]]] Where I expected [ [2, 4], [3, 5]] What am I missing? While repr should be unambiguous and is more meant for internal use and debugging. When implementing a date/time abstraction, the str can be "2010/4/12 15:35:22", etc. By pythontutorial.net.All Rights Reserved. This should be second nature. Programmers with prior experience in languages with a toString method tend to implement __str__ and not __repr__. This is explained quite well in the Python documentation: repr(object): Return a string containing a printable representation of an object. Difference between __str__ and __repr__ in Python, docs.python.org/reference/datamodel.html#object.__repr__, https://www.pythoncentral.io/what-is-the-difference-between-, How terrifying is giving a conference talk? 6) __repr__() can call repr() which will attempt to avoid infinite recursion automatically, replacing an already represented object with . On page 358 of the book Python scripting for computational science by Hans Petter Langtangen, it clearly states that. using eval or by typing it in character-for-character in a Python shell. but you wouldnt necessarily want to display that to a user. 589). This method is called by the built-in print (), str (), and format () functions. Python says "__repr__" is used to get a string representation of object while __str__" is used to find the "informal" string representation of an object. 00:30 The __repr__() method returns the canonical representation of an object in python. And what otherwise cringe-worthy stuff am I doing? Excellent answers already cover the difference between __str__ and __repr__, which for me boils down to the former being readable even by an end user, and the latter being as useful as possible to developers. You always want to use repr() [or %r formatting character, equivalently] inside __repr__ implementation, or youre defeating the goal of repr. You can implement the __str__() method in any manner. Please, This doesn't seem to answer the question of, How terrifying is giving a conference talk? Youll see when it is appropriate to use each dunder method and how some of the built-in Python functions use the two. Specifically, it is not intended to be unambiguous notice that str(3)==str("3"). Rivers of London short about Magical Signature. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Understand __str__ and __repr__ intuitively and permanently distinguish them at all. Here, you can observe that the string returned by the __str__() method is Aditya. This means that I do believe, with religious fervor, in logging. building upon the above example by "bitoffdev" and @deadly we can see how, Shouldn't it be something along the lines of. On the other hand, you should use the __str__() method to produce a human-readable representation of the object that has no use in the program apart from informing the user. Let's see an example with datetime.datetime.now(). On the other hand, repr() or __repr__ mainly returns canonical string representation of objects which serve the purpose of debugging and development helps the programmers. They are the Pythonic way to control how objects are converted to strings in different situations. Developers need (value + origin) whereas customers need a value and they don't care how they got it! The __str__ method is useful for a string representation of the object, either when someone codes in str(your_object), or even when someone might do print(your_object). @NarenYellavula if you're exposing a UUID to a customer you're probably doing something wrong. It's not super human-readable, but someone familiar with what to expect will know what this means. built-in classes from the Python standard library are doing here. The __repr__ method is present either when doing something like repr (your_object), or when a programmer might actually just type the object directly into the interpreter. Do any democracies with strong freedom of expression have laws against religious desecration? You should always avoid overriding the __repr__() method. Become a Member to join the conversation. 00:16 01:06 The .__repr__ () and .__str__ () methods are two of the special methods that you can define for any class. What is the motivation for infinity category theory? warnings.warn("urllib3 ({}) or chardet ({}) doesn't match a supported ", File "/home/aditya1117/PycharmProjects/pythonProject/webscraping.py", line 9, in
