Go ahead and test it to see the difference. Second way: Using string string.format method. Preventing a line break in Python 2 requires that you append a trailing comma to the expression: However, that’s not ideal because it also adds an unwanted space, which would translate to end=' ' instead of end='' in Python 3. 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. Sometimes you can add parentheses around the message, and they’re completely optional: At other times they change how the message is printed: String concatenation can raise a TypeError due to incompatible types, which you have to handle manually, for example: Compare this with similar code in Python 3, which leverages sequence unpacking: There aren’t any keyword arguments for common tasks such as flushing the buffer or stream redirection. Anyways, it’s always best to compare actual dictionaries before serialization. By redirecting one or both of them, you can keep things clean. Let’s take a look at an example. Your countdown should work as expected now, but don’t take my word for it. 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. In this case, you want to mock print() to record and verify its invocations. How do you debug that? Swapping them out will still give the same result: Conversely, arguments passed without names are identified by their position. It’s probably the least used of them all. The truth is that neither tracing nor logging can be considered real debugging. Tracing the state of variables at different steps of the algorithm can give you a hint where the issue is. In other words, you wouldn’t be able to print a statement or assign it to a variable like this: Here are a few more examples of statements in Python: Note: Python 3.8 brings a controversial walrus operator (:=), which is an assignment expression. After all, you don’t want to expose sensitive data, such as user passwords, when printing objects. Finally, Python Date Format Example is over. Sure, you have linters, type checkers, and other tools for static code analysis to assist you. That injected mock is only used to make assertions afterward and maybe to prepare the context before running the test. There’s a funny explanation of dependency injection circulating on the Internet: When you go and get things out of the refrigerator for yourself, you can cause problems. However, you can mitigate some of those problems with a much simpler approach. How to print current date and time using Python? Surprisingly, the signature of pprint() is nothing like the print() function’s one. Formatting output using the format method : The format() method was added in Python(2.6). It usually doesn’t have a visible representation on the screen, but some text editors can display such non-printable characters with little graphics. For more information on working with files in Python, you can check out Reading and Writing Files in Python (Guide). Almost there! print(f'{name} is {age} years old') Python f-strings are available since Python 3.6. There are external Python packages out there that allow for building complex graphical interfaces specifically to collect data from the user. You’re able to quickly diagnose problems in your code and protect yourself from them. Note: Looping over lines in a text file preserves their own newline characters, which combined with the print() function’s default behavior will result in a redundant newline character: There are two newlines after each line of text. You can make a really simple stop motion animation from a sequence of characters that will cycle in a round-robin fashion: The loop gets the next character to print, then moves the cursor to the beginning of the line, and overwrites whatever there was before without adding a newline. Sometimes logging or tracing will be a better solution. The default value of this parameter is '\n,' i.e., the new line character. However, it solves one problem while introducing another. However, not all characters allow for this–only the special ones. This may help in situations like this, when you need to analyze a problem after it happened, in an environment that you don’t have access to. This requires the use of a semicolon, which is rarely found in Python programs: While certainly not Pythonic, it stands out as a reminder to remove it after you’re done with debugging. See the Library Reference for more information on this.) Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo, <_io.TextIOWrapper name='' mode='r' encoding='UTF-8'>, <_io.TextIOWrapper name='' mode='w' encoding='UTF-8'>, <_io.TextIOWrapper name='' mode='w' encoding='UTF-8'>. How? It interprets the left argument much like a printf()-style format string to be applied to the right argument. Nonetheless, it’s a separate stream, whose purpose is to log error messages for diagnostics. Python gives you a lot of freedom when it comes to defining your own data types if none of the built-in ones meet your needs. To mock print() in a test case, you’ll typically use the @patch decorator and specify a target for patching by referring to it with a fully qualified name, that is including the module name: This will automatically create the mock for you and inject it to the test function. Sometimes there are parts of a text that you do not control, maybe they come from a database, or user input? Some of their features include: Demonstrating such tools is outside of the scope of this article, but you may want to try them out. You can’t use them to name your variables or other symbols. For example, default encoding in DOS and Windows is CP 852 rather than UTF-8, so running this can result in a UnicodeEncodeError or even garbled output: However, if you ran the same code on a system with UTF-8 encoding, then you’d get the proper spelling of a popular Russian name: It’s recommended to convert strings to Unicode as early as possible, for example, when you’re reading data from a file, and use it consistently everywhere in your code. before and after the decimal point. One way to fix this is by using the built-in zip(), sum(), and map() functions. You can test this with the following code snippet: Notice there’s a space between the words hello and AFTER: In order to get the expected result, you’d need to use one of the tricks explained later, which is either importing the print() function from __future__ or falling back to the sys module: This will print the correct output without extra space: While using the sys module gives you control over what gets printed to the standard output, the code becomes a little bit more cluttered. Calling Print Function. 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. You’re stuck with what you get. That’s why positional arguments need to follow strictly the order imposed by the function signature: print() allows an arbitrary number of positional arguments thanks to the *args parameter. Let’s say you wanted to redefine print() so that it doesn’t append a trailing newline. String Formatting. Python print format value interpolation. We place this inside the curly braces for an f-string, after the value we want to f… It’s kind of like the Heisenberg principle: you can’t measure and observe a bug at the same time. The second and more usable way of formatting strings in Python is the str.format function which is part of the string class. So, let us see how can we print both 1D as well as 2D NumPy arrays in Python. 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 … Note: To remove the newline character from a string in Python, use its .rstrip() method, like this: This strips any trailing whitespace from the right edge of the string of characters. One more interesting example could be exporting data to a comma-separated values (CSV) format: This wouldn’t handle edge cases such as escaping commas correctly, but for simple use cases, it should do. However, you can redirect log messages to separate files, even for individual modules! Nevertheless, there are times when it’s absolutely necessary. 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. The differences become apparent as you start feeding it more complex data structures: The function applies reasonable formatting to improve readability, but you can customize it even further with a couple of parameters. brightness_4 The last option you have is importing print() from future and patching it: Again, it’s nearly identical to Python 3, but the print() function is defined in the __builtin__ module rather than builtins. It tells Python that we are actually calling the function and not referring it by its name. 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. If you now loop this code, the snake will appear to be growing instead of moving. Finally, when the countdown is finished, it prints Go! In terms of semantics, the end parameter is almost identical to the sep one that you saw earlier: Now you understand what’s happening under the hood when you’re calling print() without arguments. 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. Krunal 1018 posts 201 comments. To hide it, just call one of the configuration functions defined in the module: Let’s define the snake as a list of points in screen coordinates: The head of the snake is always the first element in the list, whereas the tail is the last one. Typically, performant code tends to be more verbose: The controversy behind this new piece of syntax caused a lot of argument. The subject, however, wouldn’t be complete without talking about its counterparts a little bit. Note: To redirect stderr, you need to know about file descriptors, also known as file handles. Dictionaries often represent JSON data, which is widely used on the Internet. Because it prints in a more human-friendly way, many popular REPL tools, including JupyterLab and IPython, use it by default in place of the regular print() function. Printing isn’t thread-safe in Python. The library hides the complexities of having to deal with different terminals. While its y-coordinate stays at zero, its x-coordinate decreases from head to tail. According to those rules, you could be “printing” an SOS signal indefinitely in the following way: In Python, you can implement it in merely ten lines of code: Maybe you could even take it one step further and make a command line tool for translating text into Morse code? frozenset() function allows lists to be immutable. If you don’t care about not having access to the original print() function, then you can replace it with pprint() in your code using import renaming: Personally, I like to have both functions at my fingertips, so I’d rather use something like pp as a short alias: At first glance, there’s hardly any difference between the two functions, and in some cases there’s virtually none: That’s because pprint() calls repr() instead of the usual str() for type casting, so that you may evaluate its output as Python code if you want to. This happens to lists and tuples, for example. Note: Don’t try using print() for writing binary data as it’s only well suited for text. One way is by explicitly naming the arguments when you’re calling the function, like this: Since arguments can be uniquely identified by name, their order doesn’t matter. There were a number of good reasons for that, as you’ll see shortly. The format() function is similar to the String format method. In the previous subsection, you learned that print() delegates printing to a file-like object such as sys.stdout. I personally got to know about some of those through the Python Bytes Podcast. Since it modifies the state of a running terminal, it’s important to handle errors and gracefully restore the previous state. This article mainly focuses on the multiple ways by which can format the data before printing it out on the console. In the next subsection, you’ll discover how not having print() as a function caused a lot of headaches. When you know the remaining time or task completion percentage, then you’re able to show an animated progress bar: First, you need to calculate how many hashtags to display and how many blank spaces to insert. However, you can add a small delay to have a sneak peek: This time the screen went completely blank for a second, but the cursor was still blinking. Some regulations enforce that customer data be kept for as long as five years! However, it doesn’t come with a graphical interface, so using pdb may be a bit tricky. You apologize sincerely and make a refund, but also don’t want this to happen again in the future. But that doesn’t solve the problem, does it? Classic examples include updating the progress of a long-running operation or prompting the user for input. However, they’re encoded using hexadecimal notation in the bytes literal. For instance, you can take advantage of it for dependency injection: Here, the log parameter lets you inject a callback function, which defaults to print() but can be any callable. To this purpose, the modulo operator % is overloaded by the string class to perform string formatting. 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. Standard output is both line-buffered and block-buffered, depending on which event comes first. Other than that, it has great support for keyboard events, which might be useful for writing video games. You just import and configure it in as little as two lines of code: You can call functions defined at the module level, which are hooked to the root logger, but more the common practice is to obtain a dedicated logger for each of your source files: The advantage of using custom loggers is more fine-grain control. You need to know that there are three kinds of streams with respect to buffering: Unbuffered is self-explanatory, that is, no buffering is taking place, and all writes have immediate effect. Take a look at this example, which manifests a rounding error: As you can see, the function doesn’t return the expected value of 0.1, but now you know it’s because the sum is a little off. While print() is about the output, there are functions and libraries for the input. pprint() automatically sorts dictionary keys for you before printing, which allows for consistent comparison. 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. Note: Following other languages and frameworks, Python 3.7 introduced data classes, which you can think of as mutable tuples. In the upcoming subsection, you’ll learn how to intercept and redirect the print() function’s output. It is good to know various types for print formatting as you code more and more, so that you can print them in best way possible. Note: To toggle pretty printing in IPython, issue the following command: This is an example of Magic in IPython. This tutorial will get you up to speed with using Python print() effectively. Some of them, such as named tuples and data classes, offer string representations that look good without requiring any work on your part. With logging, you can keep your debug messages separate from the standard output. This function comes with a parameter called 'end.' First, you can take the traditional path of statically-typed languages by employing dependency injection. You’ll often want to display some kind of a spinning wheel to indicate a work in progress without knowing exactly how much time’s left to finish: Many command line tools use this trick while downloading data over the network. Unlike statements, functions are values. close, link 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. Up until now, you only dealt with built-in data types such as strings and numbers, but you’ll often want to print your own abstract data types. If you’re looking for an error, you don’t want to see all the warnings or debug messages, for example. Finally, a single print statement doesn’t always correspond to a single call to sys.stdout.write(). If you’re still reading this, then you must be comfortable with the concept of threads. Note: Debugging is the process of looking for the root causes of bugs or defects in software after they’ve been discovered, as well as taking steps to fix them. The semantics of .__str__() and .__repr__() didn’t change since Python 2, but you must remember that strings were nothing more than glorified byte arrays back then. You can do this manually, but the library comes with a convenient wrapper for your main function: Note, the function must accept a reference to the screen object, also known as stdscr, that you’ll use later for additional setup. Well, you don’t have to worry about newline representation across different operating systems when printing, because print() will handle the conversion automatically. According to the official PEP 8 style guide, you should just pick one and keep using it consistently. Here’s a quick comparison of the available functions and what they do: As you can tell, it’s still possible to simulate the old behavior in Python 3. Formatters work by putting in one or more replacement fields or placeholders — defined by a pair of curly braces {} — into a string and calling the str.format() method. Now, you can use Python’s string .format () method to obtain the same result, like this: >>>. Metaprogramming with Metaclasses in Python, User-defined Exceptions in Python with Examples, Regular Expression in Python with Examples | Set 1, Regular Expressions in Python – Set 2 (Search, Match and Find All), Python Regex: re.search() VS re.findall(), Counters in Python | Set 1 (Initialization and Updation), Basic Slicing and Advanced Indexing in NumPy Python, Random sampling in numpy | randint() function, Random sampling in numpy | random_sample() function, Random sampling in numpy | ranf() function, Random sampling in numpy | random_integers() function. Python print format December 1, 2017 admin 0 Comments. Krunal Lathiya is an Information Technology Engineer. Here, you used the string modulo operator in Python to format the string. No. Please write to us at contribute@geeksforgeeks.org to report any issue with the above content. The symbol ‘b’ after the colon inside the parenthesis notifies to display a number in binary format. and terminates the line.