The general syntax for using the str.format function is: format(value[, format_spec]) In this way of … As 1 consists only of one digit, the output is padded with 1 leading blanks. and terminates the line. We got you covered. Here, you have the exact date and time, the log level, the logger name, and the thread name. The symbol ‘b’ after the colon inside the parenthesis notifies to display a number in binary format. Maybe you’re debugging an application running in a remote web server or want to diagnose a problem in a post-mortem fashion. 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. This is followed by the total number of digits the string should contain. Python format() function Python Server Side Programming Programming The format() method formats some specified value and insert them inside … Yet, when he checked his bank account, the money was gone. Nevertheless, it’s always a good practice to archive older logs. 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. A line-buffered stream waits before firing any I/O calls until a line break appears somewhere in the buffer, whereas a block-buffered one simply allows the buffer to fill up to a certain size regardless of its content. 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 this example, printing is completely disabled by substituting print() with a dummy function that does nothing. 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 … To specify a level of precision, we need to use a colon (:), followed by a decimal point, along with some integer representing the degree of precision. python, Recommended Video Course: The Python print() Function: Go Beyond the Basics, Recommended Video CourseThe Python print() Function: Go Beyond the Basics. Compared to other programming languages, logging in Python is simpler, because the logging module is bundled with the standard library. There were a number of good reasons for that, as you’ll see shortly. 'ascii' codec can't encode character u'\xfc'... Help on built-in function print in module __builtin__: print(value, ..., sep=' ', end='\n', file=sys.stdout), <__main__.Person object at 0x7fcac3fed1d0>, '<__main__.Person object at 0x7fcac3fed1d0>', b'\xd0\xbd\xd0\xb8\xd0\xba\xd0\xb8\xd1\x82\xd0\xb0', [1, 2, 3, ], '[0, 1, 1024, 59049, 1048576, 9765625, ...]', {"username": "jdoe", "password": "s3cret"}, "\e[38;2;0;0;0m\e[48;2;255;255;255mBlack on white\e[0m", 'Downloading app.js\nDownloading style.css\n', 'Type "help", "exit", "add a [b [c ...]]"', Click here to get our free Python Cheat Sheet, Reading and Writing Files in Python (Guide), The Python print() Function: Go Beyond the Basics, Deal with newlines, character encodings, and buffering, Build advanced user interfaces in the terminal. Thread safety means that a piece of code can be safely shared between multiple threads of execution. Besides, it requires you to make changes in the code, which isn’t always possible. By default, python's print() function ends with a newline. 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. You know how to print fixed or formatted messages onto the screen. The number will be printed with 2 characters. On some occasions you might have started your program with a list instead of tuples because of the conclusion that mutable data structure is more suitable for the project. When you connect to a remote server to execute commands over the SSH protocol, each of your keystrokes may actually produce an individual data packet, which is orders of magnitude bigger than its payload. Finally, Python Date Format Example is over. 实例. Nevertheless, there are times when it’s absolutely necessary. Please write to us at contribute@geeksforgeeks.org to report any issue with the above content. According to the official PEP 8 style guide, you should just pick one and keep using it consistently. When you stop at a breakpoint, that little pause in program execution may mask the problem. For simple objects without any logic, whose purpose is to carry data, you’ll typically take advantage of namedtuple, which is available in the standard library. 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. Those magic methods are, in order of search: The first one is recommended to return a short, human-readable text, which includes information from the most relevant attributes. To check if your terminal understands a subset of the ANSI escape sequences, for example, related to colors, you can try using the following command: My default terminal on Linux says it can display 256 distinct colors, while xterm gives me only 8. Moreover, Printing tables within python is quite a challenge sometimes, as the trivial options provide you the output in an unreadable format. The truth is that neither tracing nor logging can be considered real debugging. By default, print() is bound to sys.stdout through its file argument, but you can change that. For example, in Java and C#, you have two distinct functions, while other languages require you to explicitly append \n at the end of a string literal. As with any function, it doesn’t matter whether you pass a literal, a variable, or an expression. Unlike many other functions, however, print() will accept anything regardless of its type. 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. To enable the print() function in Python 2, you need to add this import statement at the beginning of your source code: From now on the print statement is no longer available, but you have the print() function at your disposal. Note: A context switch means that one thread halts its execution, either voluntarily or not, so that another one can take over. You may use it for game development like this or more business-oriented applications. Similarly, the pprint module has an additional pformat() function that returns a string, in case you had to do something other than printing it. However, there are ways to make it look cool. First, it’ll look like this: However, after the second call to print(), the same line will appear on the screen as: As with sep, you can use end to join individual pieces into a big blob of text with a custom separator. What monkey patching does is alter implementation dynamically at runtime. The general syntax for a format placeholder is: Let’s take a look at the placeholders in our example. In a more common scenario, you’d want to communicate some message to the end user. 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. You can call print() multiple times like this to add vertical space. 1. Even though it’s a fairly simple function, you can’t test it easily because it doesn’t return a value. Python HOWTOs in-depth documents on specific topics. So, let us see how can we print both 1D as well as 2D NumPy arrays in Python. However, prepare for a deep dive as you go through the sections. 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. They complement each other. Numerous examples gave you insight into its evolution from Python 2. The string modulo operator ( % ) is still available in Python(3.x) and the user is using it widely. close, link However, a more Pythonic way of mocking objects takes advantage of the built-in mock module, which uses a technique called monkey patching. You need to explicitly convert the number to string first, in order to join them together: Unless you handle such errors yourself, the Python interpreter will let you know about a problem by showing a traceback. Here’s what you have to do: So, when you add sep=’ ‘as another argument in the print function, it disables the softspace feature and the output will look like this: As you can observe, there’s no space after the string and number 2. Learn Python 3 print() format string using {} curly braces, % and format function. Python Setup and Usage how to use Python on different platforms. Paradoxically, however, that same function can help you find bugs during a related process of debugging you’ll read about in the next section. As personal computers got more sophisticated, they had better graphics and could display more colors. Understanding the signature is only the beginning, however. 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. This is currently the most portable way of printing a newline character in Python: If you were to try to forcefully print a Windows-specific newline character on a Linux machine, for example, you’d end up with broken output: On the flip side, when you open a file for reading with open(), you don’t need to care about newline representation either. Arguments can be passed to a function in one of several ways. The line above would show up in your terminal window. You do that by inserting print statements with words that stand out in carefully chosen places. 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. Decimal value of 0.1 turns out to have an infinite binary representation, which gets rounded. To control such values, add placeholders (curly brackets {}) in the text, and run the values through the format… Either way, I hope you’re having fun with this! String format() The format() method allows you to format selected parts of a string.. You need to remember the quirky syntax instead. To find out what constitutes a newline in your operating system, use Python’s built-in os module. In Python, there is no printf() function but the functionality of the ancient printf is contained in Python. edit 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. print("Python is fun.") For example, to reset all formatting, you would type one of the following commands, which use the code zero and the letter m: At the other end of the spectrum, you have compound code values. The library hides the complexities of having to deal with different terminals. It’s probably the least used of them all. Just call the binary file’s .write() directly: If you wanted to write raw bytes on the standard output, then this will fail too because sys.stdout is a character stream: You must dig deeper to get a handle of the underlying byte stream instead: This prints an uppercase letter A and a newline character, which correspond to decimal values of 65 and 10 in ASCII. In this case, you should be using the getpass() function instead, which masks typed characters. Get a short & sweet Python Trick delivered to your inbox every couple of days. You can call it directly on any object, for example, a number: Built-in data types have a predefined string representation out of the box, but later in this article, you’ll find out how to provide one for your custom classes. If you run this program now, you won’t see any effects, because it terminates immediately. That’s because you have to erase the screen explicitly before each iteration. Printing isn’t thread-safe in Python. Python | Pandas Dataframe/Series.head() method, Python | Pandas Dataframe.describe() method, Dealing with Rows and Columns in Pandas DataFrame, Python | Pandas Extracting rows using .loc[], Python | Extracting rows using Pandas .iloc[], Python | Pandas Merging, Joining, and Concatenating, Python | Working with date and time using Pandas, Python | Read csv using pandas.read_csv(), Python | Working with Pandas and XlsxWriter | Set – 1. There are also a few other useful functions in textwrap for text alignment you’d find in a word processor. By mocking it, which you already know about from an earlier section: First, you need to store the original .write() method in a variable, which you’ll delegate to later. String Formatting. #!/usr/bin/python # -*- coding: UTF-8 -*- print("网站名： {name}, 地址 {url}".format(name="菜鸟教程", url="www.runoob.com")) # 通过字典设置参数 site = {"name": "菜鸟教程", "url": "www.runoob.com"} print("网站名： {name}, 地址 {url}".format(**site)) # 通过列表索引设置参数 my_list = ['菜鸟教程', 'www.runoob.com'] print("网站名： {0 [0]}, 地址 {0 [1]}".format(my_list)) # "0" 是必须的. It has to be either a string or None, but the latter has the same effect as the default space: If you wanted to suppress the separator completely, you’d have to pass an empty string ('') instead: You may want print() to join its arguments as separate lines. By now, you know a lot of what there is to know about print()! It usually doesn’t have a visible representation on the screen, but some text editors can display such non-printable characters with little graphics. However, it has a narrower spectrum of applications, mostly in library code, whereas client applications should use the logging module. This way, you can assign a function to a variable, pass it to another function, or even return one from another. 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. The initial shape of the snake is horizontal, starting from the top-left corner of the screen and facing to the right. 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. To disable it, you can take advantage of yet another keyword argument, end, which dictates what to end the line with. You’ll notice that you get a slightly different sequence each time: Even though sys.stdout.write() itself is an atomic operation, a single call to the print() function can yield more than one write. What’s your #1 takeaway or favorite thing you learned? However, the other one should provide complete information about an object, to allow for restoring its state from a string. You rarely call mocks in a test, because that doesn’t make much sense. Doing it manually will result in a well-known TypeError if at least one of the elements isn’t a string: It’s safer to just unpack the sequence with the star operator (*) and let print() handle type casting: Unpacking is effectively the same as calling print() with individual elements of the list. We can very easily interpolate values of any type in our print formats. Nowadays, it’s expected that you ship code that meets high quality standards. print('{} is {} years old'.format(name, age)) Since Python 3.0, the format() function was introduced to provide advance formatting options. Be aware, however, that many interpreter flavors don’t have the GIL, where multi-threaded printing requires explicit locking. a = 5 # Two objects are passed print("a =", a) b = a # Three objects are passed print('a =', a, '= b') Output. However, the default value of end still applies, and a blank line shows up. What an overhead! There are sophisticated tools for log aggregation and searching, but at the most basic level, you can think of logs as text files. No matter how hard you try, writing to the standard output seems to be atomic. To animate text in the terminal, you have to be able to freely move the cursor around. Automated parsing, validation, and sanitization of user data, Predefined widgets such as checklists or menus, Deal with newlines, character encodings and buffering. 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. 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. Here they are: Nonetheless, it’s worth mentioning a command line tool called rlwrap that adds powerful line editing capabilities to your Python scripts for free. Some streams, however, buffer certain I/O operations to enhance performance, which can get in the way. Note: The atomic nature of the standard output in Python is a byproduct of the Global Interpreter Lock, which applies locking around bytecode instructions. Note: To redirect stderr, you need to know about file descriptors, also known as file handles. Watch it together with the written tutorial to deepen your understanding: The Python print() Function: Go Beyond the Basics. These NumPy arrays can also be multi-dimensional. Even the built-in help() function isn’t that helpful with regards to the print statement: Trailing newline removal doesn’t work quite right, because it adds an unwanted space. Despite injecting a mock to the function, you’re not calling it directly, although you could. before and after the decimal point. The code under test is a function that prints a greeting. Despite being used to indicate an absence of a value, it will show up as 'None' rather than an empty string: How does print() know how to work with all these different types? Now that you know all this, you can make interactive programs that communicate with users or produce data in popular file formats. 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. Enjoy free courses, on us â†’, by Bartosz Zaczyński How are you going to put your newfound skills to use? See the Library Reference for more information on this.) There are a few ways to achieve this. 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. 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. It wouldn’t harm to include them as they’d just get ignored. Using a Single Formatter : Formatters work by putting in one or more replacement fields and placeholders defined by a pair of curly braces { } into a string and calling the str.format(). You had to install it separately: Other than that, you referred to it as mock, whereas in Python 3 it’s part of the unit testing module, so you must import from unittest.mock. How to print current date and time using Python? 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. basics The module comes with a pre-defined array class that can hold values of same type. You’ll use this technique later for mocking print() in unit tests: If you got to this point, then you’re left with only one keyword argument in print(), which you’ll see in the next subsection. 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. By using our site, you Our float number 05.333 has to be formatted with 5 characters. These tags are mixed with your content, but they’re not visible themselves. They’re arbitrary, albeit constant, numbers associated with standard streams. Python is quite a powerful language when it comes to its data science capabilities. 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. 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. Each thread will make a few print() calls with its name and a letter: A, B, and C. If you read the mocking section before, then you may already have an idea of why printing misbehaves like that. It’s less elegant than dependency injection but definitely quick and convenient. For more information on rounding numbers in Python, you can check out How to Round Numbers in Python. To disable the newline, you must specify an empty string through the end keyword argument: Even though these are two separate print() calls, which can execute a long time apart, you’ll eventually see only one line. To print multiple elements in Python 2, you must drop the parentheses around them, just like before: If you kept them, on the other hand, you’d be passing a single tuple element to the print statement: Moreover, there’s no way of altering the default separator of joined elements in Python 2, so one workaround is to use string interpolation like so: That was the default way of formatting strings until the .format() method got backported from Python 3. While the built-in format() function is a low level implementation for formatting an object using __format__() internally, string format() is a higher level implementation able to perform complex formatting operations on multiple object strings as well. 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. >>> a = 1 >>> b = 1.2 >>> c = "Python" >>> print(a, b, c, sep=",") We will obtain the following result when we run this script: That looks cleaner, right? Think of stream redirection or buffer flushing, for example. In the next subsection, you’ll discover how not having print() as a function caused a lot of headaches. Think about sending messages over a high-latency network, for example. In that case, simply pass the escaped newline character described earlier: A more useful example of the sep parameter would be printing something like file paths: Remember that the separator comes between the elements, not around them, so you need to account for that in one way or another: Specifically, you can insert a slash character (/) into the first positional argument, or use an empty string as the first argument to enforce the leading slash. First, the syntax for stream redirection uses chevron (>>) instead of the file argument. Please use ide.geeksforgeeks.org, generate link and share the link here. Keep reading to take full advantage of this seemingly boring and unappreciated little function. Functions are so-called first-class objects or first-class citizens in Python, which is a fancy way of saying they’re values just like strings or numbers. 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. The command would return a negative number if colors were unsupported. Go ahead and test it to see the difference. str.format(*args, **kwargs) The template string can be a string literal or it can contains replacement fields using {} as delimiter. These methods aren’t mutually exclusive. There are many reasons for testing software. Python is fun. All the log messages go to the standard error stream by default, which can conveniently show up in different colors. But that doesn’t solve the problem, does it? I briefly touched upon the thread safety issue before, recommending logging over the print() function. Also known as print debugging or caveman debugging, it’s the most basic form of debugging. Tracing the state of variables at different steps of the algorithm can give you a hint where the issue is. Python: Make it immutable. Formatting output using the format method : The format() method was added in Python(2.6). Other than that, it doesn’t spare you from managing character encodings properly. At the same time, there are plenty of third-party packages, which offer much more sophisticated tools. Take a look at this example, which calls an expensive function once and then reuses the result for further computation: This is useful for simplifying the code without losing its efficiency. Join us and get access to hundreds of tutorials, hands-on video courses, and a community of expert Pythonistas: Real Python Comment Policy: The most useful comments are those written with the goal of learning from or helping out other readers—after reading the whole article and all the earlier comments. In this article, we shall see how to print data to the console using python. To compare ASCII character codes, you may want to use the built-in ord() function: Keep in mind that, in order to form a correct escape sequence, there must be no space between the backslash character and a letter!