The print() function holds a reference to the standard output, which is a shared global variable. To set foreground and background with RGB channels, given that your terminal supports 24-bit depth, you could provide multiple numbers: It’s not just text color that you can set with the ANSI escape codes. 实例. There are two ways we can do this: we can specify how many significant figures we want overall, or we can specify how many significant figures we want after the decimal point. You need to get a handle of its lower-level layer, which is the standard output, and call it directly: Alternatively, you could disable buffering of the standard streams either by providing the -u flag to the Python interpreter or by setting up the PYTHONUNBUFFERED environment variable: Note that print() was backported to Python 2 and made available through the __future__ module. However, you need to declare that your test function accepts a mock now. They could barely make any more noises than that, yet video games seemed so much better with it. Finally, this is all you need to play the snake game in Python: This is merely scratching the surface of the possibilities that the curses module opens up. Consider this class with both magic methods, which return alternative string representations of the same object: If you print a single object of the User class, then you won’t see the password, because print(user) will call str(user), which eventually will invoke user.__str__(): However, if you put the same user variable inside a list by wrapping it in square brackets, then the password will become clearly visible: That’s because sequences, such as lists and tuples, implement their .__str__() method so that all of their elements are first converted with repr(). Still, for the most flexibility, you’ll have to define a class and override its magic methods described above. To check if it prints the right message, you have to intercept it by injecting a mocked function: Calling this mock makes it save the last message in an attribute, which you can inspect later, for example in an assert statement. print("Python is fun.") You can use Python’s string literals to visualize these two: The first one is one character long, whereas the second one has no content. This value will be passed through in the same place that your placeholder is positioned when you run the program.Let’s print out a string that uses a formatter:In the example above, we construc… The "%" operator is used to format a set of variables enclosed in a "tuple" (a fixed size list), together with a format string, which contains normal text together with "argument specifiers", special symbols like … Arguments can be passed to a function in one of several ways. There are several ways to format output. You rarely call mocks in a test, because that doesn’t make much sense. Defects can make their way to the production environment and remain dormant for a long time, until that one day when a branch of code finally gets executed. Or, in programmer lingo, you’d say you’ll be familiar with the function signature. In HTML you work with tags, such as or , to change how elements look in the document. Congratulations! With this site we try to show you the most common use-cases covered by the old and new style string formatting API with practical examples.. All examples on this page work out of the box with with Python 2.7, 3.2, 3.3, 3.4, and 3.5 without requiring any additional libraries. It turns out that only its head really moves to a new location, while all other segments shift towards it. Conversely, the logging module is thread-safe by design, which is reflected by its ability to display thread names in the formatted message: It’s another reason why you might not want to use the print() function all the time. Note: A dependency is any piece of code required by another bit of code. This happens to lists and tuples, for example. This way, you get the best of both worlds: The syntax for variable annotations, which is required to specify class fields with their corresponding types, was defined in Python 3.6. Mocking in Python can be done twofold. It has a side-effect. In a slightly alternative solution, instead of replacing the entire print() function with a custom wrapper, you could redirect the standard output to an in-memory file-like stream of characters: This time the function explicitly calls print(), but it exposes its file parameter to the outside world. Python Setup and Usage how to use Python on different platforms. Please use ide.geeksforgeeks.org, generate link and share the link here. Apart from that, there’s really only a handful of debugger-specific commands that you want to use for stepping through the code. Note: Following other languages and frameworks, Python 3.7 introduced data classes, which you can think of as mutable tuples. Curated by the Real Python team. If you’re still reading this, then you must be comfortable with the concept of threads. There are two of those in our example: “%2d” and “%5.2f”. The string modulo operator ( % ) is still available in Python(3.x) and the user is using it widely. Take a look at this example: If you now create an instance of the Person class and try to print it, you’ll get this bizarre output, which is quite different from the equivalent namedtuple: It’s the default representation of objects, which comprises their address in memory, the corresponding class name and a module in which they were defined. However, the default value of end still applies, and a blank line shows up. You often want your threads to cooperate by being able to mutate a shared resource. Later in this tutorial, you’ll learn how to use this mechanism for printing custom data types such as your classes. Note: str() is a global built-in function that converts an object into its string representation. This makes it always available, so it may be your only choice for performing remote debugging. It tells Python that we are actually calling the function and not referring it by its name. Therefore, it is often called a string modulo (or sometimes even called modulus) operator. Let’s create a Python snake simulator: First, you need to import the curses module. On the other hand, once you master more advanced techniques, it’s hard to go back, because they allow you to find bugs much quicker. The open() function in Python 2 lacks the encoding parameter, which would often result in the dreadful UnicodeEncodeError: Notice how non-Latin characters must be escaped in both Unicode and string literals to avoid a syntax error. There are a few libraries that provide such a high level of control over the terminal, but curses seems to be the most popular choice. Similarly, the pprint module has an additional pformat() function that returns a string, in case you had to do something other than printing it. In this example, printing is completely disabled by substituting print() with a dummy function that does nothing. It’s probably the least used of them all. For more information on working with files in Python, you can check out Reading and Writing Files in Python (Guide). To convert your objects into proper Unicode, which was a separate data type, you’d have to provide yet another magic method: .__unicode__(). Well, the short answer is that it doesn’t. Even though it’s a fairly simple function, you can’t test it easily because it doesn’t return a value. Anyways, it’s always best to compare actual dictionaries before serialization. Nonetheless, it’s a separate stream, whose purpose is to log error messages for diagnostics. Library Reference keep this under your pillow. That’s better than a plain namedtuple, because not only do you get printing right for free, but you can also add custom methods and properties to the class. Lastly, you can define multi-line string literals by enclosing them between ''' or """, which are often used as docstrings. However, the other one should provide complete information about an object, to allow for restoring its state from a string. Despite injecting a mock to the function, you’re not calling it directly, although you could. However, you have a few other options: Stream redirection is almost identical to the example you saw earlier: There are only two differences. ; The replacement field can be a numeric index of the arguments provided, or they can be keyword based arguments. In the latter case, you want the user to type in the answer on the same line: Many programming languages expose functions similar to print() through their standard libraries, but they let you decide whether to add a newline or not. The format method of strings requires more manual effort. 'Please wait while the program is loading...', can only concatenate str (not "int") to str, sequence item 1: expected str instance, int found, Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod. In the upcoming sections, you’ll see why. Specifically, when you’re printing to the standard output and the standard error streams at the same time. That’s why redefining or mocking the print statement isn’t possible in Python 2. Also, notice the use of Python’s raw strings due to backslash characters present in the literal. See your article appearing on the GeeksforGeeks main page and help other Geeks. They complement each other. In the case of print(), that side-effect is showing a message on the standard output or writing to a file. If you really need to, perhaps for legacy systems, you can use the encoding argument of open(): Instead of a real file existing somewhere in your file system, you can provide a fake one, which would reside in your computer’s memory. That changed a few decades ago when people at the American National Standards Institute decided to unify it by defining ANSI escape codes. Python format function allows printing a number in binary style. It seems as if you have more control over string representation of objects in Python 2 because there’s no magic .__unicode__() method in Python 3 anymore. Internally, both methods call __format__() method of an object.. All the log messages go to the standard error stream by default, which can conveniently show up in different colors. However, not all characters allow for this–only the special ones. UTF-8 is the most widespread and safest encoding, while unicode_escape is a special constant to express funky characters, such as é, as escape sequences in plain ASCII, such as \xe9. Second way: Using string string.format method. Secondly, you could extract that message into its own variable with a meaningful name to enhance readability and promote code reuse: Lastly, you could pass an expression, like string concatenation, to be evaluated before printing the result: In fact, there are a dozen ways to format messages in Python. This is done by indenting certain lines, inserting newlines, reordering elements, and so forth. Pretty-printing is about making a piece of data or code look more appealing to the human eye so that it can be understood more easily. After reading this section, you’ll understand how printing in Python has improved over the years. Since it modifies the state of a running terminal, it’s important to handle errors and gracefully restore the previous state. It accepts data from the standard input stream, which is usually the keyboard: The function always returns a string, so you might need to parse it accordingly: The prompt parameter is completely optional, so nothing will show if you skip it, but the function will still work: Nevertheless, throwing in a descriptive call to action makes the user experience so much better. You can’t monkey patch the print statement in Python 2, nor can you inject it as a dependency. Your countdown should work as expected now, but don’t take my word for it. When you write tests, you often want to get rid of the print() function, for example, by mocking it away. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. If you’re like most Python users, including me, then you probably started your Python journey by learning about print(). To find out exactly what features are available to you, inspect the module: You could also call dir(__future__), but that would show a lot of uninteresting internal details of the module. Let’s assume you wrote a command-line interface that understands three instructions, including one for adding numbers: At first glance, it seems like a typical prompt when you run it: But as soon as you make a mistake and want to fix it, you’ll see that none of the function keys work as expected. In fact, it also takes the input from the standard stream, but then it tries to evaluate it as if it was Python code. Nevertheless, it’s always a good practice to archive older logs. Python is fun. By using our site, you Thread safety means that a piece of code can be safely shared between multiple threads of execution. Free Bonus: Click here to get our free Python Cheat Sheet that shows you the basics of Python 3, like working with data types, dictionaries, lists, and Python functions. print() isn’t different in this regard. As with any function, it doesn’t matter whether you pass a literal, a variable, or an expression. To disable it, you can take advantage of yet another keyword argument, end, which dictates what to end the line with. Similarly, you can print this character in Python. Their specific meaning is defined by the ANSI standard. The build and deploy cycle takes time. If you can’t edit the code, you have to run it as a module and pass your script’s location: Otherwise, you can set up a breakpoint directly in the code, which will pause the execution of your script and drop you into the debugger. In the example above, you’re interested in the side-effect rather than the value, which evaluates to None, so you simply ignore it. To eliminate that side-effect, you need to mock the dependency out. 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The string has the f prefix and uses {} to evaluate variables. Concatenation, end statement & mathematic operation inside print() function. This is followed by the total number of digits the string should contain. Note: You might have heard the terms: dummy, fake, stub, spy, or mock used interchangeably. It’s less elegant than dependency injection but definitely quick and convenient. Does that mean you should be using the print statement as if it were a function? To do actual debugging, you need a debugger tool, which allows you to do the following: A crude debugger that runs in the terminal, unsurprisingly named pdb for “The Python Debugger,” is distributed as part of the standard library. We can very easily interpolate values of any type in our print formats. This number includes the decimal point and all the digits, i.e. We place this inside the curly braces for an f-string, after the value we want to f… However, it solves one problem while introducing another. You’re able to quickly diagnose problems in your code and protect yourself from them. The decimal part of the number or the precision is set to 2, i.e. Note: In Python 3, the pass statement can be replaced with the ellipsis (...) literal to indicate a placeholder: This prevents the interpreter from raising IndentationError due to missing indented block of code. One last reason to switch from the print() function to logging is thread safety. Note: It’s customary to put the two instructions for spinning up a debugger on a single line. You may be asking yourself if it’s possible to convert an object to its byte string representation rather than a Unicode string in Python 3. In Python 2.7, print is a statement; this means that print (" {}").format ("testing") prints one expression, the result of the expression (" {}").format ("testing"). But if you think that’s all there is to know about Python’s print() function, then you’re missing out on a lot! Similarly, escape codes won’t show up in the terminal as long as it recognizes them. However, a more Pythonic way of mocking objects takes advantage of the built-in mock module, which uses a technique called monkey patching. That’s very handy in a common case of message formatting, where you’d want to join a few elements together. Code 2: The following diagram with an example usage depicts how the format method works for positional parameters: Formatting output using the String method : This output is formatted by using string slicing and concatenation operations. In the previous subsection, you learned that print() delegates printing to a file-like object such as sys.stdout. Go ahead and type this command to see if your terminal can play a sound: This would normally print text, but the -e flag enables the interpretation of backslash escapes.