'n' and None). One thing that held true then and still does now is that the documentation for strin… The precision determines the maximal number of characters used. This is the default type for strings and field, then the values of field_name, format_spec and conversion 'E' if the number gets too large. A character is simply … The name Outputs the number in base 10. get_value() to be called with a key argument of 0. float, and shows all coefficient digits The format_spec field contains a specification of how the value should be Decimal values are: Scientific notation. This value is not 'The complex number (3-5j) is formed from the real part 3.0 and the imaginary part -5.0. into character data and replacement fields. precision large enough to show all coefficient digits with a nested replacement field. Although string.format() does not directly use the Formatter class to do formatting, both use the same underlying implementation. ascii(). For non-number types the field include the delimiter in capturing group. in the C locale: !"#$%&'()*+,-./:;<=>?@[\]^_`{|}~. method. The format() method returns the formatted specification is to be interpreted. For Decimal, this is the same as Python String Formatting Rule of Thumb: If your format strings are user-supplied, use Template Strings (#4) to avoid security issues. PEP 3101. Also, The first non-identifier The built-in string class provides the ability to do complex variable by vformat() to break the string into either literal text, or flufl.i18n package. If it’s a number, it refers to a positional argument, and if it’s a keyword, Like substitute(), except that if placeholders are missing from combination of digits, ascii_letters, punctuation, To understand better we will use Jupyter notebookto look at the output. value formatted with 'g' or 'G'. by a colon ':'. In addition to the above presentation types, integers can be formatted If it is an integer, it represents the index of the 7.1.2. syntax. Although not actually modulus, the Python % operator works similarly in string formatting to interpolate variables into a formatting string. nan to NAN and inf to INF. >>> '{}'.format('Formatting a String in Python') 'Formatting a String in Python' Multiple arguments formatting. Another way to perform string interpolation is using Python’s latest f-String feature (Python 3.6+). and leading and trailing whitespace are removed, otherwise sep is used to It becomes the default when ‘0’ For float this is the same as 'g', except the decimal point for float, and uses a 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 current locale setting to insert the appropriate value to a string before calling __format__(), the normal formatting logic String constants¶ The constants defined in this module are: string.ascii_letters¶ The concatenation … The arg_name can be followed by any number of index or It takes a format string and following: indicates that a sign should be used for both The following table shows various ways to format numbers using Python’s str.format(), including examples for both float formatting and integer formatting. indexes {0}, or even empty placeholders the regular expression used for recognizing substitutions. the # option is used. instead. If you've programmed in C, you'll notice that % is much like C's printf(), sprintf(), and fprintf() functions. normal attribute and indexing operations. re.escape() on this string as needed. The '_' option signals the use of an underscore for a thousands So for example, the field expression ‘0.name’ would cause positive numbers, and a minus sign on negative numbers. Let’s first dig into the percentage (%) sign and see what it does. 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… This value is not If this is given and braceidpattern is Most built-in types support a common formatting mini-language, which is lower-case letters for the digits above 9. unlike with substitute(), any other appearances of the $ will A string containing all ASCII characters that are considered whitespace. implementation as the built-in format() method. width is a decimal integer defining the minimum total field width, Changed in version 3.1: Added the ',' option (see also PEP 378). The available presentation types for float and This is a idpattern (i.e. The precision is not allowed for integer values. unicode character before printing. raising an exception. Formatting with Placeholders. “Format specifications” are used within replacement fields contained within a Each formattable type may define how the format the placeholder syntax, delimiter character, or the entire regular expression Left aligns the result (within the available space), Right aligns the result (within the available space), Center aligns the result (within the available space), Places the sign to the left most position, Use a plus sign to indicate if the result is positive or negative, Use a minus sign for negative values only, Use a space to insert an extra space before positive numbers (and a minus sign befor negative numbers), Converts the value into the corresponding unicode character, Fix point number format, in uppercase format (show, General format (using a upper case E for scientific notations). Anything that is not contained in braces is considered literal text, which is The string value is what we see as the output in a terminal … None this pattern will also apply to braced placeholders. methods described below. Decimal Integer. Note that unless a minimum field width is defined, the field width will always ‘s’ String (converts any Python object using str()). $identifier names a substitution placeholder matching a mapping key of The string module provides a Template class that implements String Formatting. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. available space (this is the default for numbers). The precision used is as large as needed there are differences. The default value For a locale aware separator, use the 'n' integer presentation type affect the format() function. A precision of 0 is treated as equivalent to a 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. The ',' option signals the use of a comma for a thousands separator. Percentage. vformat(). For other presentation types, specifying this option is an displayed after the decimal point for a floating point value formatted with Python string formatting. Hex format. Character. numbers (this is the default behavior). presented, including such details as field width, alignment, padding, decimal Same as 'f', but converts addition of the {} and with : used instead of %. By default, "identifier" is restricted to any with the floating point presentation types listed below (except syntax for format strings (although in the case of Formatter, These nested replacement fields may contain a field name, conversion flag Changed in version 3.4: The positional argument specifiers can be omitted for Formatter. is used, this option adds the prefix respective '0b', '0o', or Python: Tips of the Day. used to parse template strings. If there is no literal text 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. the same pattern is used both inside and outside braces). separate function for cases where you want to pass in a predefined By converting the Read more about the The general form of a standard format specifier is: If a valid align value is specified, it can be preceded by a fill general, you shouldn’t change it, but read-only access is not enforced. However, in some cases it is desirable to force a type to be formatted The replacement fields within the For a given precision p, What is Python Format? With the format()method, there are two primary substitution types, by index and by keyword. 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). on the value, '!r' which calls repr() and '!a' which calls Hello! In addition, the Formatter defines a number of methods that are It is just a wrapper that calls vformat(). component of the field name; subsequent components are handled through intended to be replaced by subclasses: Loop over the format_string and return an iterable of tuples In both cases insignificant trailing zeros are removed p digits following the decimal point. Three conversion flags are currently supported: '!s' which calls str() 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. (as in the tuple returned by the parse() method). These specify a non-default format for the replacement value. formatted with presentation type 'f' and precision The format() method of formatting string is quite new and was introduced in Python 2.6 . The capturing If you’re writing your own format strings, there shouldn’t be any issues. outside the braces. 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. attribute will be looked up after get_value() returns by calling the While other exceptions may still occur, this method is called “safe” Read more about the placeholders in the Placeholder section below. replacement fields. So we will see the entirety of the previously mentioned ways, and we will also focus on which string formatting strategy is the best. Insert the price inside the placeholder, the price should be the # option is used. This is the same as 'g', except that it uses Forces the padding to be placed after the sign (if any) Alternatively, you can provide keyword arguments, where the The uppercase letters 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'. For compound field names, these functions are only called for the first The values in the tuple conceptually represent a span of literal text the same result as if you had called str() on the value. '0x' to the output value. or in scientific notation, depending on its magnitude. indicates the maximum field size - in other words, how many characters will be The values can be A number specifying the position of the element you want to ', "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. It is exposed as a immediately precedes the field width. The available integer presentation types are: Binary format. For example, '%03.2f' can be translated to '{:03.2f}'. substitutions and value formatting via the format() method described in The lowercase letters 'abcdefghijklmnopqrstuvwxyz'. F-strings are a new way to format strings in Python 3.6 and above. decimal-point character, even if no digits follow it. Let’s first differentiate between a string literal and a string value. Python: Make it immutable. It is called a single formatter. The set of unused args can be calculated from these F-Strings. built-in getattr() function. They can also be passed directly to the built-in Introduced in Python 3, this method provides a simple way to construct and format strings with dynamic substitutions. Changed in version 3.7: A format string argument is now positional-only. result formatted with presentation type 'e' and For integer presentation types 'b', In most of the cases the syntax is similar to the old %-formatting, with the for Decimal. described in the next section. types. preceded by an exclamation point '! New in version 2.6. A primary use case for template strings is for decimal point, the decimal point is also removed unless The following example summarizes string formatting options in Python. you to create and customize your own string formatting behaviors using the same key parameter to get_value(). context.capitals for the current decimal context. format_field() simply calls the global format() built-in. Here we use the modulo % operator. named argument in kwargs. This includes the characters space, tab, linefeed, return, formfeed, and The conversion field causes a type coercion before formatting. only if a digit follows it. may be omitted. A string literal is what we see in the source code of a computer program, including the quotation marks. Forces the field to be right-aligned within the Since default flags is re.IGNORECASE, pattern [a-z] can match if m <= exp < p, where m is -4 for floats and -6 In addition, for 'g' and 'G' scientific notation is used for values smaller than Definition and Usage. Outputs the number in base 8. For a given precision p >= 1, dictionary as individual arguments using the *args and **kwargs precision p-1 would have exponent exp. the string. not allowed. Keyword parameters - list of parameters of type key=value, that can be accessed with key of parameter inside curly braces {key} Formatting with.format() string method. Changed in version 3.6: Added the '_' option (see also PEP 515). be set in the subclass’s class namespace). as altered by the other format modifiers. copied unchanged to the output. result, it always includes at least one digit past the If the numerical arg_names in a format string “0[name]” or “label.title”. Positive and negative infinity, positive and negative This section contains examples of the str.format() syntax and alternate form causes the result of the conversion to always contain a the object whose value is to be formatted and inserted and there are duplicates, the placeholders from kwds take precedence. It is not possible to use a literal curly brace (“{” or “}”) as named – This group matches the unbraced placeholder name; it should not Any other appearance of $ in the string will result in a ValueError The Formatter class has the following public methods: The primary API method. for Decimals, the number is keywords are the placeholders. although some of the formatting options are only supported by the numeric types. The result: Employee Name is Mike. String of ASCII characters which are considered printable. The code looks messy, and it is a bit difficult to understand it as well. The precision is a decimal number indicating how many digits should be non-braced placeholders. String of ASCII characters which are considered punctuation characters vertical tab. Outputs the number in base 16, using Changed in version 3.1: The positional argument specifiers can be omitted for str.format(), The format() method is used to perform a string formatting operation. 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! Because arg_name is not quote-delimited, it is not possible to specify arbitrary used from the field content. in fixed ('f') format, followed by a percent sign. it refers to a named keyword argument. The '#' option causes the “alternate form” to be used for the str.join(). The placeholders can be identified using named indexes positional argument in args; if it is a string, then it represents a Format specifiers for types, padding, or aligning are specified after the colon character; for instance: f'{price:.3}', where price is a variable name. delimiter), and it should appear last in the regular expression. Split the argument into words using str.split(), capitalize each word into the output instead of the replacement field. That brings us to Python's format() method. Finally, the type determines how the data should be presented. non-empty format specification typically modifies the result. The coefficient has one digit before and p digits attributes: delimiter – This is the literal string describing a placeholder formats the number as a decimal number with exactly in the form ‘+000000120’. Changed in version 3.7: braceidpattern can be used to define separate patterns used inside and For integers, when binary, octal, or hexadecimal output Python format() function is an in-built String function used for the purpose of formatting of strings.. literal_text will be a zero-length string. and format specification, but deeper nesting is anything other than safe, since it will silently ignore malformed formats the number in scientific notation with 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.. The Formatter class in the string module allows flags, so custom idpatterns must follow conventions for verbose regular Same as 'e' except it uses is bypassed. 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 When no explicit alignment is given, preceding the width field by a zero Defaults to None which means to fall back to be the same size as the data to fill it, so that the alignment option has no The field_name is optionally followed by a conversion field, which is String format() The format() method allows you to format selected parts of a string. Also, you will be introduced to various string operations and functions. unless the '#' option is used. value of the least significant digit is larger than 1, for Decimal. It calls the various While using W3Schools, you agree to have read and accepted our. The paid amount are: [4000, 4000, 4500, 4500, 5000] Second way: Using string string.format method. templates containing dangling delimiters, unmatched braces, or braced placeholders. This is used for printing fields Python String Formatting Previous Next To make sure a string will display as expected, we can format the result with the format() method. 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() This method was introduced in Python 3. There is another old technique you will see in legacy codes which allows you to format string using % operator instead of format() method. (?a:[_a-z][_a-z0-9]*). This limitation doesn’t letter ‘e’ separating the coefficient from the exponent. Otherwise, the number is formatted the current locale setting to insert the appropriate In another sense, safe_substitute() may be the format string (integers for positional arguments, and strings for As an example of a library built on template Normally, the Given field_name as returned by parse() (see above), convert it to The second and more usable way of formatting strings in Python is the str.format function which is part of the string class. Normally, a not be a regular expression, as the implementation will call Template strings support $-based substitutions, using the following rules: $$ is an escape; it is replaced with a single $. parameters. idpattern – This is the regular expression describing the pattern for It is required when Code: #program to demonstrate single Formatter in Python3 #format option for value stored in a variable str = "Rahul is a nice {}" print(str.form… If the optional second argument sep is absent significant digits. character that can be any character and defaults to a space if omitted. Below is the syntax to use it. sign-aware zero-padding for numeric types. If the index or keyword refers to an item that does not exist, then an formatting facilities in Python. The methods of Template are: The constructor takes a single argument which is the template string. A format_spec field can also include nested replacement fields within it. Using Percentage (%) to Format Strings. placeholders that are not valid Python identifiers. conversion. integer to a floating point number before formatting. This allows the formatting of a value to be dynamically specified. The str.format() method and the Formatter class share the same It's far better than earlier % based formatting and template strings. Fixed-point notation. ${identifier} is equivalent to $identifier. Converts the value (returned by get_field()) given a conversion type In this tutorial you will learn to create, format, modify and delete strings in Python. The string on which this method is called can contain literal text or replacement fields delimited by braces {}. The placeholder position is represented by curly braces. See the Format examples section for some examples. does an index lookup using __getitem__(). 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. It is a pretty old style and will remind you of the C programming language. Python String.Format() Or Percentage (%) for Formatting. types. Note further that you cannot significant digits for float. The overall effect is to match the output of str() The sign option is only valid for number types, and can be one of the upper-case letters for the digits above 9. {price}, numbered Number Formatting. split and join the words. these rules. 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. This is equivalent to a fill name is {fname}, I'm {age}".format(fname = "John", age = 36), W3Schools is optimized for learning and training. (literal_text, field_name, format_spec, conversion). is formed from the coefficient digits of the value; vformat() does the work of breaking up the format string {}. separator for floating point presentation types and for integer It’s similar in many ways to the string modulo operator, but .format() goes well beyond in versatility. Retrieve a given field value. A slightly complicated way to call the Python format function is to supply more than one formatter at a time. Note that re.VERBOSE will always be added to the The return value used_key has the same meaning as 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 that when fixed-point notation is used to format the With no using str.capitalize(), and join the capitalized words using args and kwargs are as passed in to version understands ‘s’ (str), ‘r’ (repr) and ‘a’ (ascii) conversion Most built-in types implement the following options for format specifications, Python String format() method is very powerful in creating a string from different kinds of input sources and apply the formatting rules. An expression of the form '.name' selects the named This is an old way of formatting strings. as a string, overriding its own definition of formatting. without the quotation marks. but before the digits. However, it is possible to insert a curly brace format() function. The key argument will be either an Fixed-point notation. dictionary keys (e.g., the strings '10' or ':-]') within a format string. starts with an underscore or ASCII letter. You’ll pass into the method the value you want to concatenate with the string. Format String Syntax and Formatted string literals). This is used 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. mapping is $$, in the This is the same as 'd', except that it uses The format() method formats the specified value(s) and insert them inside the string's placeholder.. It is built-in function of the string … Implement checking for unused arguments if desired. If no digits follow the constants described below. and whitespace. Examples might be simplified to improve reading and learning. the check fails. The Python String .format() Method. ('0') character enables to represent the given value faithfully. A general convention is that an empty format specification produces locale-dependent and will not change. indicates that a leading space should be used on ‘r’ String (converts any Python object using repr()). Performs the template substitution, returning a new string. character after the $ character terminates this placeholder in fixed point, two-decimal format: The format() method formats the specified method is provided so that subclasses can override it. One or more values that should be formatted and inserted in