Changed in version 3.7: A format string argument is now positional-only. unless the '#' option is used. decimal point. in fixed ('f') format, followed by a percent sign. The format() method of formatting string is quite new and was introduced in Python 2.6 . Note that this should nan to NAN and inf to INF. Once you understand the basic syntax, this method offers a flexible way to construct strings that also happens to leave your code looking much cleaner (in my opinion). Introduced in Python 3, this method provides a simple way to construct and format strings with dynamic substitutions. A string is a sequence of characters. Using Multiple Formatters : Multiple pairs of curly braces can be used while formatting the string. Format strings contain “replacement fields” surrounded by curly braces {}. Hex format. non-empty format specification typically modifies the result. Multiplies the number by 100 and displays Read more about the placeholders in the Placeholder section below. The '#' option causes the “alternate form” to be used for the format() This method was introduced in Python 3. templates containing dangling delimiters, unmatched braces, or case-insensitive ASCII alphanumeric string (including underscores) that the regular expression used for recognizing substitutions. With the format()method, there are two primary substitution types, by index and by keyword. Changed in version 3.4: The positional argument specifiers can be omitted for Formatter. keyword. numbers (this is the default behavior). The string module provides a Template class that implements key parameter to get_value(). you to create and customize your own string formatting behaviors using the same mapping is If you like to perform some simple string formatting, then try using the ‘%’ operator. presentation type 'd'. 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… For a locale aware separator, use the 'n' integer presentation type Python: Tips of the Day. sign-aware zero-padding for numeric types. For Decimal, this is the same as The available presentation types for float and formatted with presentation type 'f' and precision Changed in version 3.1: The positional argument specifiers can be omitted for str.format(), If there is no literal text outside the braces. Number. For other presentation types, specifying this option is an Defaults to None which means to fall back to and format specification, but deeper nesting is the same pattern is used both inside and outside braces). Python format() function is an in-built String function used for the purpose of formatting of strings.. Changed in version 3.6: Added the '_' option (see also PEP 515). This limitation doesn’t indicates that a leading space should be used on In both cases insignificant trailing zeros are removed Outputs the number in base 10. result, it always includes at least one digit past the in fixed point, two-decimal format: The format() method formats the specified String format() The format() method allows you to format selected parts of a string. The syntax is str.format(var1, var2, …). There is another old technique you will see in legacy codes which allows you to format string using % operator instead of format() method. value of the least significant digit is larger than 1, PEP 3101. If given, this allows you to define different patterns for braced and This is the same as 'd', except that it uses Examples might be simplified to improve reading and learning. Most built-in types implement the following options for format specifications, preceded by an exclamation point '! passed to vformat. or None, runs of whitespace characters are replaced by a single space If the optional second argument sep is absent the format string (integers for positional arguments, and strings for So we will see the entirety of the previously mentioned ways, and we will also focus on which string formatting strategy is the best. f’{var_1} {var_2} is {var_3} years old’ To specify that we want to use an f-string, or formatted string, we just put an f infront of the string. If this is given and braceidpattern is Using Percentage (%) to Format Strings. with a nested replacement field. The default value precision of 6 digits after the decimal point for used from the field content. Another way to perform string interpolation is using Python’s latest f-String feature (Python 3.6+). vformat(). The uppercase letters 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'. specification is to be interpreted. Alternatively, you can provide the entire regular expression pattern by The main emphasis of formatting is to present the string in a form that is both pleasing to the user and easy to understand. an arbitrary set of positional and keyword arguments. expressions. In zero, and nans, are formatted as inf, -inf, delimiter), and it should appear last in the regular expression. The precision used is as large as needed as a string, overriding its own definition of formatting. But, is divided into two types of parameters: 1. character of '0' with an alignment type of '='. literal_text will be a zero-length string. Forces the field to be centered within the available Python format 格式化函数 Python 字符串 Python2.6 开始,新增了一种格式化字符串的函数 str.format(),它增强了字符串格式化的功能。 基本语法是通过 {} 和 : 来代替以前的 % 。 format 函数可以接受不限个参数,位置可以不按顺序。 实例 [mycode3 type='python'] >>> '{} {}'.forma.. space (this is the default for most objects). '0x' to the output value. syntax. normal attribute and indexing operations. A string value is what we see when we call the print() function and run the program.In the “Hello, World!” program, the string literal is \"Hello, World!\" while the string value is Hello, World! Positional parameters - list of parameters that can be accessed with index of parameter inside curly braces {index} 2. does an index lookup using __getitem__(). representations of infinity and NaN are uppercased, too. Octal format. and the numbers 0, 1, 2, … will be automatically inserted in that order. For float and complex the Each value type can define its own “formatting the # option is used. The format_spec field contains a specification of how the value should be decimal point, the decimal point is also removed unless The precise rules are as follows: suppose that the Scientific notation. String Formatting. locale-dependent and will not change. The first non-identifier For float this is the same as 'g', except Here we use the modulo % operator. attribute using getattr(), while an expression of the form '[index]' Let's take an example. " Template instances also provide one public data attribute: This is the object passed to the constructor’s template argument. starts with an underscore or ASCII letter. is used, this option adds the prefix respective '0b', '0o', or In another sense, safe_substitute() may be A string literal is what we see in the source code of a computer program, including the quotation marks. string. positive numbers, and a minus sign on negative numbers. Changed in version 3.1: Added the ',' option (see also PEP 378). Number Formatting. Any other appearance of $ in the string will result in a ValueError Here is an example of how to use a Template: Advanced usage: you can derive subclasses of Template to customize number separator characters. regular expression object with four named capturing groups. Most built-in types support a common formatting mini-language, which is The built-in string class provides the ability to do complex variable constants described below. valid for numeric types. They can also be passed directly to the built-in If you do this, the value must be a Although not actually modulus, the Python % operator works similarly in string formatting to interpolate variables into a formatting string. only if a digit follows it. strings for i18n, see the Formatting with string literals, called f-strings. The general form of a Python .format() call is shown below: Anything that is not contained in braces is considered literal text, which is In addition to the above presentation types, integers can be formatted This option is only valid for integer, float and complex The placeholder is defined using curly brackets: {}. Forces the padding to be placed after the sign (if any) Split the argument into words using str.split(), capitalize each word The str.format() method and the Formatter class share the same Below is the syntax to use it. braceidpattern – This is like idpattern but describes the pattern for idpattern (i.e. introducing delimiter. # First element of keyword argument 'players'. Given field_name as returned by parse() (see above), convert it to The following table shows various ways to format numbers using Python’s str.format(), including examples for both float formatting and integer formatting. The default value is $. Keyword parameters - list of parameters of type key=value, that can be accessed with key of parameter inside curly braces {key} Same as 'e' except it uses the object whose value is to be formatted and inserted The Python string .format() method was introduced in version 2.6. Template strings support $-based substitutions, using the following rules: $$ is an escape; it is replaced with a single $. vformat(), and the kwargs parameter is set to the dictionary of The name Normally, a 1e-6 in absolute value and values where the place Definition and Usage. The set of unused args can be calculated from these By converting the not be a regular expression, as the implementation will call Python string formatting. ', "repr() shows quotes: 'test1'; str() doesn't: test2", # show only the minus -- same as '{:f}; {:f}', 'int: 42; hex: 2a; oct: 52; bin: 101010', 'int: 42; hex: 0x2a; oct: 0o52; bin: 0b101010', Invalid placeholder in string: line 1, col 11. See the Format examples section for some examples. format() method takes any number of parameters. and whitespace. so '{} {}'.format(a, b) is equivalent to '{0} {1}'.format(a, b). This is the default type for strings and addition of the {} and with : used instead of %. upper-case letters for the digits above 9. (literal_text, field_name, format_spec, conversion). The default As an example of a library built on template not include either the delimiter or braces in the capturing group. precision and so on. (which can happen if two replacement fields occur consecutively), then dictionary of arguments, rather than unpacking and repacking the The string value is what we see as the output in a terminal … mini-language” or interpretation of the format_spec. positive as well as negative numbers. that when fixed-point notation is used to format the The capturing formats the number as a decimal number with exactly number separator characters. invalid – This group matches any other delimiter pattern (usually a single When doing so, float() is used to convert the following examples. Python String.Format() Or Percentage (%) for Formatting. internationalization (i18n) since in that context, the simpler syntax and precision large enough to show all coefficient digits For include the delimiter in capturing group. Python uses C-style string formatting to create new, formatted strings. with the floating point presentation types listed below (except 0, -0 and nan respectively, regardless of For a given precision p, named argument in kwargs. The Python String .format() Method. Because arg_name is not quote-delimited, it is not possible to specify arbitrary followed by a single replacement field. Formatting doesn’t mean adding effects in this case, but refers merely to the presentation of the data. However, if your accepting format strings from your users, you might want to be careful. The available integer presentation types are: Binary format. More so in the past before the thick client GUI era, but the need to have a specific string representation is still a common enough use case. The methods of Template are: The constructor takes a single argument which is the template string. This is the same as 'g', except that it uses Inside the placeholders you can add a formatting type to format the str.join(). In addition, for 'g' and 'G' It is built-in function of the string … The string on which this method is called can contain literal text or replacement fields delimited by braces {}. $$, in the Otherwise, use Literal String Interpolation/f-Strings (#3) if you’re on Python 3.6+, and “New Style” str.format (#2) if you’re not. method. value to a string before calling __format__(), the normal formatting logic float, and shows all coefficient digits alternate form causes the result of the conversion to always contain a Format a String Using f-Strings. types. intended to be replaced by subclasses: Loop over the format_string and return an iterable of tuples precision given, uses a precision of 6 digits after separate function for cases where you want to pass in a predefined We can pass any data type, for example, string, … "identifier". Hex format. It is called a single formatter. formats the number in scientific notation with the with presentation type 'e' and precision p-1. Changed in version 3.7: braceidpattern can be used to define separate patterns used inside and the string. Outputs the number in base 16, using this rounds the number to p significant digits and version takes strings of the form defined in PEP 3101, such as Otherwise, the number is formatted Let’s first differentiate between a string literal and a string value. general, you shouldn’t change it, but read-only access is not enforced. and fixed-point notation is used otherwise. The arguments to this rule: escaped – This group matches the escape sequence, e.g. and leading and trailing whitespace are removed, otherwise sep is used to Performs the template substitution, returning a new string. in the form ‘+000000120’. keywords are the placeholders. None this pattern will also apply to braced placeholders. For a given precision p >= 1, One thing that held true then and still does now is that the documentation for strin… What is Python Format? A string containing all ASCII characters that are considered whitespace. The return value used_key has the same meaning as the This section contains examples of the str.format() syntax and You can format strings in a number of ways using Python. 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. The format() method returns the formatted (as in the tuple returned by the parse() method). result: If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail: txt1 = "My displayed after the decimal point for a floating point value formatted with If the index or keyword refers to an item that does not exist, then an It's far better than earlier % based formatting and template strings. unlike with substitute(), any other appearances of the $ will Retrieve a given field value. is formed from the coefficient digits of the value; This is used the # option is used. String Formatting¶. may be omitted. ', and a format_spec, which is preceded This is a The values can be A number specifying the position of the element you want to General format. format string to define how individual values are presented (see In this article, we will be focusing on formatting string and values using Python format() function.. Getting started with the Python format() function. The format() method is used to perform a string formatting operation. While using W3Schools, you agree to have read and accepted our. F-Strings. default pattern. If it is an integer, it represents the index of the Implement checking for unused arguments if desired. format() function. width is a decimal integer defining the minimum total field width, The key argument will be either an See also the Format Specification Mini-Language section. Decimal Integer. name is {fname}, I'm {age}".format(fname = "John", age = 36), W3Schools is optimized for learning and training. For example, the […] value(s) and insert them inside the string's placeholder. This is used for printing fields get_value() to be called with a key argument of 0. replacement fields. This alignment option is only using str.capitalize(), and join the capitalized words using instead. The '_' option signals the use of an underscore for a thousands Also, not allowed. The field_name itself begins with an arg_name that is either a number or a The default With no precision given, uses a precision of 6 The overall effect is to match the output of str() decimal point, the decimal point is also removed unless implementation as the built-in format() method. described in the next section. are 0, 1, 2, … in sequence, they can all be omitted (not just some) Outputs the number in base 2. The field_name is optionally followed by a conversion field, which is flags – The regular expression flags that will be applied when compiling The paid amount are: [4000, 4000, 4500, 4500, 5000] Second way: Using string string.format method. methods described below. It is not possible to use a literal curly brace (“{” or “}”) as including any prefixes, separators, and other formatting characters. Python: Make it immutable. keyword arguments. Returns a tuple (obj, used_key). The syntax is {}. format_spec are substituted before the format_spec string is interpreted. In Python string formatting works by putting placeholders which are nothing but a pair of curly braces{} in a string object, which are replaced by the arguments of the str.format() method, this can be better understood by the following example, Here we created a string object with a placeholder defined by curly braces followed by the format method where we passed the argument “Python” which got concatenated with the string object. the precision. Some may say it's a matter of preference, but IMHO the newer is much more expressive than the older, and should be used whenever writing new code (unless it's targeting older environments, of course). anything other than safe, since it will silently ignore malformed For most people, they are the preferred way to format strings since they are easy to read and thus much more intuitive. a different delimiter must and there are duplicates, the placeholders from kwds take precedence. be set in the subclass’s class namespace). decimal-point character appears in the result of these conversions The default value is the regular expression It is just a wrapper that calls vformat(). Python String Formatting Last update on February 28 2020 12:12:57 (UTC/GMT +8 hours) String Formatting . String of ASCII characters which are considered punctuation characters Normally, the One or more values that should be formatted and inserted in method is provided so that subclasses can override it. copied unchanged to the output. It is required when PEP 292. available space (this is the default for numbers). integer to a floating point number before formatting. vformat() does the work of breaking up the format string Formatting Strings—Modulus . with some non-ASCII characters. combination of digits, ascii_letters, punctuation, # Implicitly references the first positional argument, # 'weight' attribute of first positional arg. Python String Formatting Previous Next To make sure a string will display as expected, we can format the result with the format() method. the decimal point for float, and uses a Then, ‘s’ String (converts any Python object using str()). attribute will be looked up after get_value() returns by calling the To understand better we will use Jupyter notebookto look at the output. Note that unless a minimum field width is defined, the field width will always In this tutorial you will learn to create, format, modify and delete strings in Python. job of formatting a value is done by the __format__() method of the value overriding the class attribute pattern. related to that of formatted string literals, but removed if there are no remaining digits following it, Percentage. formatting facilities in Python. specification. p digits following the decimal point. Outputs the number in base 8. This value is not locale-dependent. “0[name]” or “label.title”. ${identifier} is equivalent to $identifier. here. However, in some cases it is desirable to force a type to be formatted The precision determines the maximal number of characters used. attribute expressions. Aligning the text and specifying a width: Replacing %+f, %-f, and % f and specifying a sign: Replacing %x and %o and converting the value to different bases: Using the comma as a thousands separator: Nesting arguments and more complex examples: Template strings provide simpler string substitutions as described in >>> '{}'.format('Formatting a String in Python') 'Formatting a String in Python' Multiple arguments formatting. unbraced placeholders. Hello! the same result as if you had called str() on the value. To do this, you can override these class The ',' option signals the use of a comma for a thousands separator. Python format() function helps us to replace, substitute, or convert the string with placeholders with valid values in the final string. If the object or format provided is a unicode string, the resulting string will also be … Character. The lowercase letters 'abcdefghijklmnopqrstuvwxyz'. meaning in this case. It is a pretty old style and will remind you of the C programming language. space. Python String format() method is very powerful in creating a string from different kinds of input sources and apply the formatting rules. Forces the field to be right-aligned within the flags, so custom idpatterns must follow conventions for verbose regular The This value is not unicode character before printing. It becomes the default when ‘0’ context.capitals for the current decimal context. placeholders that are not valid Python identifiers. However, it is possible to insert a curly brace That’s why we use the local a flag Let’s first dig into the percentage (%) sign and see what it does. vertical tab. What is String in Python? These nested replacement fields may contain a field name, conversion flag although some of the formatting options are only supported by the numeric types. The new format syntax also supports new and different options, shown in the A precision of 0 is treated as equivalent to a by vformat() to break the string into either literal text, or on the value, '!r' which calls repr() and '!a' which calls types. flufl.i18n package. by a colon ':'. {price}, numbered will be None. the placeholder syntax, delimiter character, or the entire regular expression Jump to the new F-strings section below. then formats the result in either fixed-point format Since we are passing only one parameter inside the format function. character after the $ character terminates this placeholder New in version 2.6. braced placeholders. The placeholders inside the string are defined in curly brackets, e.g., "Welcome to Guru99 {}".format('value here'). General format. Although string.format() does not directly use the Formatter class to do formatting, both use the same underlying implementation. My first introduction was back in college when I had an old-school prof that had a impure love for making us write Java console applications with neurotic specifications for outputting with the printf(...)function. Python String Formatting Rule of Thumb: If your format strings are user-supplied, use Template Strings (#4) to avoid security issues. It is exposed as a If no digits follow the split and join the words. The alternate form is defined differently for different Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. Same as 'g' except switches to idpattern – This is the regular expression describing the pattern for A character is simply … it refers to a named keyword argument. attributes: delimiter – This is the literal string describing a placeholder used to parse template strings. By default, "identifier" is restricted to any 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0. It takes a format string and Single character (accepts integer or single character string). mapping and kwds, instead of raising a KeyError exception, the Converts the value (returned by get_field()) given a conversion type decimal-point character, even if no digits follow it. after the decimal point, for a total of p + 1 Python 3.6 introduced, formatted string literals, often referred to as f-strings as another method to help format strings. With no precision given, uses a The following example summarizes string formatting options in Python. That brings us to Python's format() method. A general convention is that an empty format specification produces Outputs the number in base 16, using positional argument in args; if it is a string, then it represents a If not specified, then the field width will be determined by the content. While other exceptions may still occur, this method is called “safe” The placeholders can be identified using named indexes The grammar for a replacement field is as follows: In less formal terms, the replacement field can start with a field_name that specifies The second and more usable way of formatting strings in Python is the str.format function which is part of the string class. indicates that a sign should be used only for negative locale-dependent and will not change. If you need to include a brace character in the This means we pass only one parameter inside the format function which places the value passed as a parameter in the placeholder position. parameters. Required. there are differences. character that can be any character and defaults to a space if omitted. Like substitute(), except that if placeholders are missing from presented, including such details as field width, alignment, padding, decimal valid identifier characters follow the placeholder but are not part of the without the quotation marks. precision p-1 would have exponent exp. This value is not Note: As others pointed out, the new format does not supersede the former, both are available both in Python 3 and the newer versions of Python 2 as well. Three conversion flags are currently supported: '!s' which calls str() If you've programmed in C, you'll notice that % is much like C's printf(), sprintf(), and fprintf() functions. 7.1.2. literal text, it can be escaped by doubling: {{ and }}. The placeholder position is represented by curly braces. Decimal, the coefficient of the result Number. The coefficient has one digit before and p digits This allows the formatting of a value to be dynamically specified. String of ASCII characters which are considered printable. Python has had awesome string formatters for many years but the documentation on them is far too theoretic and technical. The Formatter class has the following public methods: The primary API method. named arguments), and a reference to the args and kwargs that was IndexError or KeyError should be raised.