float, and shows all coefficient digits decimal point. Changed in version 3.1: The positional argument specifiers can be omitted for str.format(), Insert the price inside the placeholder, the price should be (literal_text, field_name, format_spec, conversion). Positional parameters - list of parameters that can be accessed with index of parameter inside curly braces {index} 2. outside the braces. The default value is the regular expression String constants¶ The constants defined in this module are: string.ascii_letters¶ The concatenation … the fill character in a formatted string literal or when using the str.format() With no It becomes the default when ‘0’ The following table shows various ways to format numbers using Python’s str.format(), including examples for both float formatting and integer formatting. 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). string. conversion. will be None. The code looks messy, and it is a bit difficult to understand it as well. Hex format. These arguments inside format method can be anything integer, str… specification. The second and more usable way of formatting strings in Python is the str.format function which is part of the string class. One thing that held true then and still does now is that the documentation for strin… named – This group matches the unbraced placeholder name; it should not Read more about the vformat(). attribute expressions. str.join(). If you've programmed in C, you'll notice that % is much like C's printf(), sprintf(), and fprintf() functions. expressions. The '#' option causes the “alternate form” to be used for the an object to be formatted. Formatting with Placeholders. Otherwise, the number is formatted Forces the field to be centered within the available The grammar for a replacement field is as follows: In less formal terms, the replacement field can start with a field_name that specifies It's far better than earlier % based formatting and template strings. this rounds the number to p significant digits and Python String Formatting Last update on February 28 2020 12:12:57 (UTC/GMT +8 hours) String Formatting . syntax for format strings (although in the case of Formatter, into character data and replacement fields. If you’re writing your own format strings, there shouldn’t be any issues. described in the next section. name is {fname}, I'm {age}".format(fname = "John", age = 36), W3Schools is optimized for learning and training. the # option is used. Python has had awesome string formatters for many years but the documentation on them is far too theoretic and technical. ascii(). Hello! and fixed-point notation is used otherwise. the same pattern is used both inside and outside braces). simply return $ instead of raising ValueError. # First element of keyword argument 'players'. mapping and kwds, instead of raising a KeyError exception, the including any prefixes, separators, and other formatting characters. separator for floating point presentation types and for integer The arg_name can be followed by any number of index or these rules. The methods of Template are: The constructor takes a single argument which is the template string. with some non-ASCII characters. regular expression object with four named capturing groups. general, you shouldn’t change it, but read-only access is not enforced. in fixed point, two-decimal format: The format() method formats the specified $$, in the “Format specifications” are used within replacement fields contained within a Template strings support $-based substitutions, using the following rules: $$ is an escape; it is replaced with a single $. For float and complex the default pattern. IndexError or KeyError should be raised. For a given precision p, indicates that a leading space should be used on braced placeholders. Changed in version 3.7: braceidpattern can be used to define separate patterns used inside and Number Formatting. For a given precision p >= 1, The Python string .format() method was introduced in version 2.6. Since default flags is re.IGNORECASE, pattern [a-z] can match Same as 'f', but converts The syntax is copied unchanged to the output. nan to NAN and inf to INF. precision p-1 would have exponent exp. significant digits for float. Decimal values are: Scientific notation. The capturing valid for numeric types. keyword. component of the field name; subsequent components are handled through precision and so on. space (this is the default for most objects). 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). It is called a single formatter. The general form of a Python .format() call is shown below: If you do this, the value must be a 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. While using W3Schools, you agree to have read and accepted our. normal attribute and indexing operations. A character is simply … Octal format. The syntax is str.format(var1, var2, …). Note further that you cannot # Implicitly references the first positional argument, # 'weight' attribute of first positional arg. The precision is not allowed for integer values. For The meaning of the various alignment options is as follows: Forces the field to be left-aligned within the available parameters. It takes a format string and dictionary as individual arguments using the *args and **kwargs presented, including such details as field width, alignment, padding, decimal 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". a different delimiter must the string. indicates that a sign should be used only for negative General format. Decimal, the coefficient of the result Formatting with.format() string method. displayed after the decimal point for a floating point value formatted with The set of unused args can be calculated from these subclasses can define their own format string syntax). precision of 6 digits after the decimal point for check_unused_args() is assumed to raise an exception if However, in some cases it is desirable to force a type to be formatted and there are duplicates, the placeholders from kwds take precedence. the same result as if you had called str() on the value. Template instances also provide one public data attribute: This is the object passed to the constructor’s template argument. These nested replacement fields may contain a field name, conversion flag The available presentation types for float and The default dictionary keys (e.g., the strings '10' or ':-]') within a format string. The field_name is optionally followed by a conversion field, which is Same as 'e' except it uses If it is an integer, it represents the index of the in the C locale: !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~. templates containing dangling delimiters, unmatched braces, or PEP 292. version understands ‘s’ (str), ‘r’ (repr) and ‘a’ (ascii) conversion presentation type 'd'. (as in the tuple returned by the parse() method). constants described below. The placeholder is defined using curly brackets: {}. If there is no replacement Python format() function is an in-built String function used for the purpose of formatting of strings.. Also, literal_text will be a zero-length string. The available integer presentation types are: Binary format. Note that unless a minimum field width is defined, the field width will always For compound field names, these functions are only called for the first A string literal is what we see in the source code of a computer program, including the quotation marks. A slightly complicated way to call the Python format function is to supply more than one formatter at a time. replacement fields. The space. locale-dependent and will not change. The sign option is only valid for number types, and can be one of the case-insensitive ASCII alphanumeric string (including underscores) that The placeholder position is represented by curly braces. precision given, uses a precision of 6 digits after Python string formatting. The overall effect is to match the output of str() {}. (?a:[_a-z][_a-z0-9]*). character after the $ character terminates this placeholder anything other than safe, since it will silently ignore malformed This is a digits. One or more values that should be formatted and inserted in method. The placeholders inside the string are defined in curly brackets, e.g., "Welcome to Guru99 {}".format('value here'). Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. {price}, numbered Any other appearance of $ in the string will result in a ValueError The uppercase letters 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'. 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 being raised. Defaults to None which means to fall back to The arguments to this Anything that is not contained in braces is considered literal text, which is format_spec are substituted before the format_spec string is interpreted. Each formattable type may define how the format separate function for cases where you want to pass in a predefined formats the number as a decimal number with exactly attributes: delimiter – This is the literal string describing a placeholder Using Percentage (%) to Format Strings. This is an old way of formatting strings. the regular expression used for recognizing substitutions. following: indicates that a sign should be used for both positive as well as negative numbers. Although string.format() does not directly use the Formatter class to do formatting, both use the same underlying implementation. The placeholder is defined using curly brackets: {}. 'o', 'x', and 'X', underscores will be inserted every 4 This allows the formatting of a value to be dynamically specified. include the delimiter in capturing group. sign-aware zero-padding for numeric types. Python: Make it immutable. built-in getattr() function. These specify a non-default format for the replacement value. followed by a single replacement field. Another way to perform string interpolation is using Python’s latest f-String feature (Python 3.6+). Format String Syntax and Formatted string literals). result formatted with presentation type 'e' and The placeholders can be identified using named indexes You can format strings in a number of ways using Python. In addition to the above presentation types, integers can be formatted Number. formatting facilities in Python. decimal point, the decimal point is also removed unless 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0. $identifier names a substitution placeholder matching a mapping key of In both cases insignificant trailing zeros are removed the check fails. are 0, 1, 2, … in sequence, they can all be omitted (not just some) related to that of formatted string literals, but and the numbers 0, 1, 2, … will be automatically inserted in that order. In this article, we will be focusing on formatting string and values using Python format() function.. Getting started with the Python format() function. or in scientific notation, depending on its magnitude. It is not possible to use a literal curly brace (“{” or “}”) as Split the argument into words using str.split(), capitalize each word Three conversion flags are currently supported: '!s' which calls str() Python String format() method is very powerful in creating a string from different kinds of input sources and apply the formatting rules. ‘s’ String (converts any Python object using str()). 0, -0 and nan respectively, regardless of Given field_name as returned by parse() (see above), convert it to The ',' option signals the use of a comma for a thousands separator. 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. Format strings contain “replacement fields” surrounded by curly braces {}. either 'g' or 'G' depending on the value of only if a digit follows it. groups correspond to the rules given above, along with the invalid placeholder Changed in version 3.4: The positional argument specifiers can be omitted for Formatter. Python String.Format() Or Percentage (%) for Formatting. original placeholder will appear in the resulting string intact. with presentation type 'e' and precision p-1. not allowed. Formatting with string literals, called f-strings. mapping is representations of infinity and NaN are uppercased, too. String Formatting¶. >>> '{}'.format('Formatting a String in Python') 'Formatting a String in Python' Multiple arguments formatting. You’ll pass into the method the value you want to concatenate with the string. The paid amount are: [4000, 4000, 4500, 4500, 5000] Second way: Using string string.format method. field, then the values of field_name, format_spec and conversion attribute using getattr(), while an expression of the form '[index]' numbers (this is the default behavior). General format. integer to a floating point number before formatting. The result: Employee Name is Mike. This is used The values in the tuple conceptually represent a span of literal text frozenset() function allows lists to be immutable. While other exceptions may still occur, this method is called “safe” intended to be replaced by subclasses: Loop over the format_string and return an iterable of tuples By converting the flags – The regular expression flags that will be applied when compiling result, it always includes at least one digit past the This section contains examples of the str.format() syntax and The alternate form is defined differently for different format_field() simply calls the global format() built-in. 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… 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. passed to vformat. context.capitals for the current decimal context. does an index lookup using __getitem__(). Python uses C-style string formatting to create new, formatted strings. The values can be A number specifying the position of the element you want to placeholders that are not valid Python identifiers. the current locale setting to insert the appropriate ‘r’ String (converts any Python object using repr()). internationalization (i18n) since in that context, the simpler syntax and locale-dependent and will not change. any dictionary-like object with keys that match the placeholders in the For other presentation types, specifying this option is an If there is no literal text It is the oldest method of string formatting. Fixed-point notation. To understand better we will use Jupyter notebookto look at the output. number separator characters. For non-number types the field split and join the words. When both mapping and kwds are given We can pass any data type, for example, string, … (which can happen if two replacement fields occur consecutively), then If not specified, then the field width will be determined by the content. integer or a string. The string on which this method is called can contain literal text or replacement fields delimited by braces {}. preceded by an exclamation point '! Required. lower-case letters for the digits above 9. Normally, the 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.. Formatting Strings—Modulus . The format() method of formatting string is quite new and was introduced in Python 2.6 . value formatted with 'g' or 'G'. literal text, it can be escaped by doubling: {{ and }}. For most people, they are the preferred way to format strings since they are easy to read and thus much more intuitive. For Decimal, this is the same as In most of the cases the syntax is similar to the old %-formatting, with the 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. version takes strings of the form defined in PEP 3101, such as methods described below. See the Format examples section for some examples. addition of the {} and with : used instead of %. Then, It calls the various If this is given and braceidpattern is for Decimal. from the significand, and the decimal point is also This is the same as 'g', except that it uses Finally, the type determines how the data should be presented. So we will see the entirety of the previously mentioned ways, and we will also focus on which string formatting strategy is the best. using str.capitalize(), and join the capitalized words using decimal-point character, even if no digits follow it. then formats the result in either fixed-point format 'f' and 'F', or before and after the decimal point for a floating point Since we are passing only one parameter inside the format function. after the decimal point, for a total of p + 1 delimiter), and it should appear last in the regular expression. named argument in kwargs. The string module provides a Template class that implements syntax. Alternatively, you can provide the entire regular expression pattern by but before the digits. The reason that string.format() does not use the Formatter class directly is because "string" is a built-in type, which means that all of its methods must be implemented in C, whereas Formatter is a Python class. vertical tab. Converts the integer to the corresponding character of '0' with an alignment type of '='. in fixed ('f') format, followed by a percent sign. Fixed-point notation. New in version 2.6. In letter ‘e’ separating the coefficient from the exponent. … This value is not 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. Python 3.6 introduced, formatted string literals, often referred to as f-strings as another method to help format strings. They can also be passed directly to the built-in be set in the subclass’s class namespace). upper-case letters for the digits above 9. This function does the actual work of formatting. The Formatter class has the following public methods: The primary API method. If the optional second argument sep is absent '0x' to the output value. This value is not Keyword parameters - list of parameters of type key=value, that can be accessed with key of parameter inside curly braces {key} The following example summarizes string formatting options in Python. If no digits follow the An expression of the form '.name' selects the named Introduced in Python 3, this method provides a simple way to construct and format strings with dynamic substitutions. is re.IGNORECASE. be the same size as the data to fill it, so that the alignment option has no idpattern – This is the regular expression describing the pattern for As an example of a library built on template The general syntax for using the str.format … starts with an underscore or ASCII letter. here. This is used for printing fields change the delimiter after class creation (i.e. conversions, trailing zeros are not removed from the result. Outputs the number in base 2. Same as 'g' except switches to format() function. attribute will be looked up after get_value() returns by calling the The replacement fields within the Python String Formatting Previous Next To make sure a string will display as expected, we can format the result with the format() method. Using Multiple Formatters : Multiple pairs of curly braces can be used while formatting the string. non-braced placeholders. It is required when Outputs the number in base 8. number separator characters. For example, the […] Python format() function helps us to replace, substitute, or convert the string with placeholders with valid values in the final string. To do this, you can override these class p-1-exp. types. Alternatively, you can provide keyword arguments, where the vformat(), and the kwargs parameter is set to the dictionary of types. introducing delimiter. It is built-in function of the string … strings for i18n, see the Changed in version 3.1: Added the ',' option (see also PEP 378). function is the set of all argument keys that were actually referred to in specification is to be interpreted. String of ASCII characters which are considered punctuation characters with a nested replacement field. Number. decimal point, the decimal point is also removed unless The conversion field causes a type coercion before formatting. get_value() to be called with a key argument of 0. formats the number in scientific notation with the Hex format. The default value is $. In another sense, safe_substitute() may be A Also, you will be introduced to various string operations and functions. although some of the formatting options are only supported by the numeric types. For float this is the same as 'g', except args and kwargs are as passed in to String Formatting. braced – This group matches the brace enclosed placeholder name; it should positional argument in args; if it is a string, then it represents a 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! Outputs the number in base 16, using String of ASCII characters which are considered printable. For example, '%03.2f' can be translated to '{:03.2f}'. Character. precision large enough to show all coefficient digits By default, "identifier" is restricted to any ', "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. idpattern (i.e. itself. The '_' option signals the use of an underscore for a thousands 1e-6 in absolute value and values where the place may be omitted. Implement checking for unused arguments if desired. an upper case ‘E’ as the separator character. not include either the delimiter or braces in the capturing group. the placeholder syntax, delimiter character, or the entire regular expression Most built-in types support a common formatting mini-language, which is is formed from the coefficient digits of the value; The constants defined in this module are: The concatenation of the ascii_lowercase and ascii_uppercase This option is only valid for integer, float and complex if m <= exp < p, where m is -4 for floats and -6 The format() method formats the specified value(s) and insert them inside the string's placeholder.. When no explicit alignment is given, preceding the width field by a zero as altered by the other format modifiers. 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 The coefficient has one digit before and p digits This is equivalent to a fill It is just a wrapper that calls vformat(). format() This method was introduced in Python 3. Jump to the new F-strings section below. positive numbers, and a minus sign on negative numbers. The available string presentation types are: String format. If the object or format provided is a unicode string, the resulting string will also be … In addition, the Formatter defines a number of methods that are Single character (accepts integer or single character string). Sooner or later string formatting becomes a necessary evil for most programmers. What is Python Format? it refers to a named keyword argument. as a string, overriding its own definition of formatting. With the format()method, there are two primary substitution types, by index and by keyword. Because arg_name is not quote-delimited, it is not possible to specify arbitrary the current locale setting to insert the appropriate This is the default type for strings and For integers, when binary, octal, or hexadecimal output because it always tries to return a usable string instead of Formatting doesn’t mean adding effects in this case, but refers merely to the presentation of the data. So for example, the field expression ‘0.name’ would cause vformat() does the work of breaking up the format string ('0') character enables Definition and Usage. There is another old technique you will see in legacy codes which allows you to format string using % operator instead of format() method. It is a pretty old style and will remind you of the C programming language. unless the '#' option is used. Note that this should job of formatting a value is done by the __format__() method of the value The main emphasis of formatting is to present the string in a form that is both pleasing to the user and easy to understand. Note that re.VERBOSE will always be added to the Format specifiers for types, padding, or aligning are specified after the colon character; for instance: f'{price:.3}', where price is a variable name. A precision of 0 is treated as equivalent to a If you like to perform some simple string formatting, then try using the ‘%’ operator. Let’s first dig into the percentage (%) sign and see what it does. 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. raising an exception. is bypassed. instead. The new format syntax also supports new and different options, shown in the keyword arguments. This includes the characters space, tab, linefeed, return, formfeed, and If the numerical arg_names in a format string The built-in string class provides the ability to do complex variable The args parameter is set to the list of positional arguments to The first non-identifier Each value type can define its own “formatting Video: Python Strings. 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. If given, this allows you to define different patterns for braced and Let’s first differentiate between a string literal and a string value. not be a regular expression, as the implementation will call character that can be any character and defaults to a space if omitted. the decimal point for float, and uses a 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. 'E' if the number gets too large. flufl.i18n package. unicode character before printing. 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. Multiplies the number by 100 and displays alternate form causes the result of the conversion to always contain a ${identifier} is equivalent to $identifier. This is the same as 'd', except that it uses used from the field content. Changed in version 3.6: Added the '_' option (see also PEP 515). and format specification, but deeper nesting is With no precision given, uses a precision of 6 Scientific notation. A string is a sequence of characters. Format a String Using f-Strings. The general form of a standard format specifier is: If a valid align value is specified, it can be preceded by a fill you to create and customize your own string formatting behaviors using the same is used, this option adds the prefix respective '0b', '0o', or Read more about the placeholders in the Placeholder section below. The str.format() method and the Formatter class share the same indicates the maximum field size - in other words, how many characters will be