placeholders that are not valid Python identifiers. Most built-in types implement the following options for format specifications, 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.. PEP 3101. Python: Tips of the Day. What is Python Format? the object whose value is to be formatted and inserted and fixed-point notation is used otherwise. attribute using getattr(), while an expression of the form '[index]' Same as 'g' except switches to constants described below. It becomes the default when ‘0’ function is the set of all argument keys that were actually referred to in preceded by an exclamation point '! separator for floating point presentation types and for integer 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. A precision of 0 is treated as equivalent to a $$, in the Python uses C-style string formatting to create new, formatted strings. positional argument in args; if it is a string, then it represents a With no This function does the actual work of formatting. A character is simply … The result: Employee Name is Mike. for Decimal. If you've programmed in C, you'll notice that % is much like C's printf(), sprintf(), and fprintf() functions. format string to define how individual values are presented (see instead. vformat(), and the kwargs parameter is set to the dictionary of only if a digit follows it. Performs the template substitution, returning a new string. In keyword arguments. A an object to be formatted. The first non-identifier Outputs the number in base 2. result formatted with presentation type 'e' and Python String.Format() Or Percentage (%) for Formatting. formatting facilities in Python. Note that this should However, it is possible to insert a curly brace although some of the formatting options are only supported by the numeric types. space (this is the default for most objects). You’ll pass into the method the value you want to concatenate with the string. None this pattern will also apply to braced placeholders. ('0') character enables followed by a single replacement field. The default value is $. 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. “Format specifications” are used within replacement fields contained within a So for example, the field expression ‘’ would cause Hello! 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. F-strings are a new way to format strings in Python 3.6 and above. parameters. without the quotation marks. Insert the price inside the placeholder, the price should be Same as 'e' except it uses However, if your accepting format strings from your users, you might want to be careful. 1e-6 in absolute value and values where the place (?a:[_a-z][_a-z0-9]*). The ',' option signals the use of a comma for a thousands separator. For example, '%03.2f' can be translated to '{:03.2f}'. remove. then formats the result in either fixed-point format For a given precision p, The format_spec field contains a specification of how the value should be The precision used is as large as needed Let's take an example. " Number. It is required when Python: Make it immutable. Defaults to None which means to fall back to not include either the delimiter or braces in the capturing group. unicode character before printing. nan to NAN and inf to INF. it refers to a named keyword argument. (as in the tuple returned by the parse() method). that when fixed-point notation is used to format the there are differences. implementation as the built-in format() method. dictionary as individual arguments using the *args and **kwargs {price}, numbered 'f' and 'F', or before and after the decimal point for a floating point The arguments to this If it’s a number, it refers to a positional argument, and if it’s a keyword, related to that of formatted string literals, but 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. 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. general, you shouldn’t change it, but read-only access is not enforced. For float and complex the the fill character in a formatted string literal or when using the str.format() Fixed-point notation. Same as 'f', but converts formats the number in scientific notation with the Template instances also provide one public data attribute: This is the object passed to the constructor’s template argument. PEP 292. This alignment option is only Formatting with Placeholders. representations of infinity and NaN are uppercased, too. check_unused_args() is assumed to raise an exception if specification is to be interpreted. This is used for printing fields If no digits follow the If you’re writing your own format strings, there shouldn’t be any issues. Changed in version 3.7: A format string argument is now positional-only. precision p-1 would have exponent exp. # Implicitly references the first positional argument, # 'weight' attribute of first positional arg. The available string presentation types are: String format. vformat() does the work of breaking up the format string This value is not One or more values that should be formatted and inserted in Formatting with string literals, called f-strings. The methods of Template are: The constructor takes a single argument which is the template string. Forces the field to be centered within the available The syntax is str.format(var1, var2, …). The Formatter class has the following public methods: The primary API method. The args parameter is set to the list of positional arguments to result, it always includes at least one digit past the methods described below. be the same size as the data to fill it, so that the alignment option has no See the Format examples section for some examples. letter ‘e’ separating the coefficient from the exponent. character of '0' with an alignment type of '='. “0[name]” or “label.title”. precision and so on. float, and shows all coefficient digits Finally, the type determines how the data should be presented. width is a decimal integer defining the minimum total field width, As an example of a library built on template Changed in version 3.1: The positional argument specifiers can be omitted for str.format(), The meaning of the various alignment options is as follows: Forces the field to be left-aligned within the available attribute will be looked up after get_value() returns by calling the the string. the same pattern is used both inside and outside braces). By converting the significant digits. The field_name itself begins with an arg_name that is either a number or a These nested replacement fields may contain a field name, conversion flag used to parse template strings. mini-language” or interpretation of the format_spec. syntax for format strings (although in the case of Formatter, The string module provides a Template class that implements The placeholder position is represented by curly braces. '0x' to the output value. However, in some cases it is desirable to force a type to be formatted ', and a format_spec, which is preceded number separator characters. indexes {0}, or even empty placeholders The conversion field causes a type coercion before formatting. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. The placeholder is defined using curly brackets: {}. for Decimals, the number is an upper case ‘E’ as the separator character. flags, so custom idpatterns must follow conventions for verbose regular {}. the current locale setting to insert the appropriate or None, runs of whitespace characters are replaced by a single space A string containing all ASCII characters that are considered whitespace. Octal format. separate function for cases where you want to pass in a predefined String of ASCII characters which are considered printable. args and kwargs are as passed in to decimal point, the decimal point is also removed unless valid identifier characters follow the placeholder but are not part of the The name decimal-point character, even if no digits follow it. including any prefixes, separators, and other formatting characters. Positive and negative infinity, positive and negative p-1-exp. The built-in str and unicode classes provide the ability to do complex variable substitutions and value formatting via the str.format() method described in PEP 3101.The Formatter class in the string module allows you to create and customize your own string formatting behaviors using the same implementation as the built-in format() method. indicates that a leading space should be used on for Decimal. Most built-in types support a common formatting mini-language, which is If the object or format provided is a unicode string, the resulting string will also be … passed to vformat. comparison with the old %-formatting. literal_text will be a zero-length string. The placeholders can be identified using named indexes $identifier names a substitution placeholder matching a mapping key of The uppercase letters 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'. Here we use the modulo % operator. Format a String Using f-Strings. A slightly complicated way to call the Python format function is to supply more than one formatter at a time. The general form of a standard format specifier is: If a valid align value is specified, it can be preceded by a fill p digits following the decimal point. A primary use case for template strings is for If not specified, then the field width will be determined by the content. The capturing When doing so, float() is used to convert the outside the braces. The key argument will be either an used from the field content. So we will see the entirety of the previously mentioned ways, and we will also focus on which string formatting strategy is the best. This means we pass only one parameter inside the format function which places the value passed as a parameter in the placeholder position. Anything that is not contained in braces is considered literal text, which is the # option is used. decimal point, the decimal point is also removed unless braced placeholders. available space (this is the default for numbers). Decimal values are: Scientific notation. The Python string .format() method was introduced in version 2.6. zero, and nans, are formatted as inf, -inf, being raised. will be None. If the numerical arg_names in a format string on the value, '!r' which calls repr() and '!a' which calls Any other appearance of $ in the string will result in a ValueError This value is not The format() method returns the formatted space. Formatting doesn’t mean adding effects in this case, but refers merely to the presentation of the data. The named – This group matches the unbraced placeholder name; it should not named arguments), and a reference to the args and kwargs that was The format() method formats the specified value(s) and insert them inside the string's placeholder.. get_value() to be called with a key argument of 0. 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 precision determines the maximal number of characters used. Decimal, the coefficient of the result In addition, for 'g' and 'G' with some non-ASCII characters. placeholder, such as "${noun}ification". following: indicates that a sign should be used for both Hex format. For a given precision p >= 1, Then, numbers (this is the default behavior). Each formattable type may define how the format format() method takes any number of parameters. This is equivalent to a fill here. or in scientific notation, depending on its magnitude. (which can happen if two replacement fields occur consecutively), then from the significand, and the decimal point is also after the decimal point, for a total of p + 1 The main emphasis of formatting is to present the string in a form that is both pleasing to the user and easy to understand. itself. New in version 2.6. Three conversion flags are currently supported: '!s' which calls str() To do this, you can override these class In addition to the above presentation types, integers can be formatted The '_' option signals the use of an underscore for a thousands The format() function. in the form ‘+000000120’. Note that re.VERBOSE will always be added to the Here is an example of how to use a Template: Advanced usage: you can derive subclasses of Template to customize Forces the padding to be placed after the sign (if any) It calls the various precision of 6 digits after the decimal point for The new format syntax also supports new and different options, shown in the 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 Outputs the number in base 10. anything other than safe, since it will silently ignore malformed following examples. The set of unused args can be calculated from these But, is divided into two types of parameters: 1. With no precision given, uses a built-in getattr() function. In this tutorial you will learn to create, format, modify and delete strings in Python. by vformat() to break the string into either literal text, or integer to a floating point number before formatting. Video: Python Strings. context.capitals for the current decimal context. Also, Jump to the new F-strings section below. # First element of keyword argument 'players'. Examples might be simplified to improve reading and learning. Single character (accepts integer or single character string). in fixed point, two-decimal format: The format() method formats the specified This limitation doesn’t Let’s first differentiate between a string literal and a string value. 'o', 'x', and 'X', underscores will be inserted every 4 decimal point. delimiter), and it should appear last in the regular expression. the regular expression used for recognizing substitutions. dictionary of arguments, rather than unpacking and repacking the 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0. Scientific notation. is used, this option adds the prefix respective '0b', '0o', or In most of the cases the syntax is similar to the old %-formatting, with the Definition and Usage. the format string (integers for positional arguments, and strings for Forces the field to be right-aligned within the String of ASCII characters which are considered punctuation characters addition of the {} and with : used instead of %. One thing that held true then and still does now is that the documentation for strin… Using Multiple Formatters : Multiple pairs of curly braces can be used while formatting the string. Also, you will be introduced to various string operations and functions. value formatted with 'g' or 'G'. For integers, when binary, octal, or hexadecimal output significant digits for float. "identifier". Python String format() method is very powerful in creating a string from different kinds of input sources and apply the formatting rules. The built-in string class provides the ability to do complex variable syntax. you to create and customize your own string formatting behaviors using the same substitutions and value formatting via the format() method described in The coefficient has one digit before and p digits these rules. If this is given and braceidpattern is Sooner or later string formatting becomes a necessary evil for most programmers. It's far better than earlier % based formatting and template strings. 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 "%s" and "%d". meaning in this case. value of the least significant digit is larger than 1, non-empty format specification typically modifies the result. These arguments inside format method can be anything integer, str… The field_name is optionally followed by a conversion field, which is For float this is the same as 'g', except In both cases insignificant trailing zeros are removed upper-case letters for the digits above 9. are 0, 1, 2, … in sequence, they can all be omitted (not just some) The Python String .format() Method. Outputs the number in base 16, using 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! case-insensitive ASCII alphanumeric string (including underscores) that introducing delimiter. not allowed. The precision is not allowed for integer values. It is built-in function of the string … You can format strings in a number of ways using Python. vformat(). For other presentation types, specifying this option is an alternate form causes the result of the conversion to always contain a method is provided so that subclasses can override it. component of the field name; subsequent components are handled through number separator characters. This value is not locale-dependent. format() This method was introduced in Python 3. Hex format. job of formatting a value is done by the __format__() method of the value braceidpattern – This is like idpattern but describes the pattern for 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). starts with an underscore or ASCII letter. Below is the syntax to use it. idpattern (i.e. removed if there are no remaining digits following it, the # option is used. The format() method of formatting string is quite new and was introduced in Python 2.6 . str.join(). types. character after the $ character terminates this placeholder They can also be passed directly to the built-in This includes the characters space, tab, linefeed, return, formfeed, and The precise rules are as follows: suppose that the Inside the placeholders you can add a formatting type to format the String Formatting. 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. because it always tries to return a usable string instead of locale-dependent and will not change. may be omitted. Alternatively, you can provide the entire regular expression pattern by In another sense, safe_substitute() may be keywords are the placeholders. A string literal is what we see in the source code of a computer program, including the quotation marks. Changed in version 3.1: Added the ',' option (see also PEP 378). described in the next section. Each value type can define its own “formatting internationalization (i18n) since in that context, the simpler syntax and as altered by the other format modifiers. with the floating point presentation types listed below (except in the C locale: !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~. original placeholder will appear in the resulting string intact. Number Formatting. Format String Syntax and Formatted string literals). Required. intended to be replaced by subclasses: Loop over the format_string and return an iterable of tuples If you like to perform some simple string formatting, then try using the ‘%’ operator. Since default flags is re.IGNORECASE, pattern [a-z] can match If no digits follow the That brings us to Python's format() method. Formatting with.format() string method. attributes: delimiter – This is the literal string describing a placeholder any dictionary-like object with keys that match the placeholders in the is formed from the coefficient digits of the value; Changed in version 3.7: braceidpattern can be used to define separate patterns used inside and idpattern – This is the regular expression describing the pattern for Python has had awesome string formatters for many years but the documentation on them is far too theoretic and technical. Python format() function helps us to replace, substitute, or convert the string with placeholders with valid values in the final string. Formatting Strings—Modulus . 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.