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diff --git a/Doc/ref/ref2.tex b/Doc/ref/ref2.tex deleted file mode 100644 index bad4609..0000000 --- a/Doc/ref/ref2.tex +++ /dev/null @@ -1,731 +0,0 @@ -\chapter{Lexical analysis\label{lexical}} - -A Python program is read by a \emph{parser}. Input to the parser is a -stream of \emph{tokens}, generated by the \emph{lexical analyzer}. This -chapter describes how the lexical analyzer breaks a file into tokens. -\index{lexical analysis} -\index{parser} -\index{token} - -Python uses the 7-bit \ASCII{} character set for program text. -\versionadded[An encoding declaration can be used to indicate that -string literals and comments use an encoding different from ASCII]{2.3} -For compatibility with older versions, Python only warns if it finds -8-bit characters; those warnings should be corrected by either declaring -an explicit encoding, or using escape sequences if those bytes are binary -data, instead of characters. - - -The run-time character set depends on the I/O devices connected to the -program but is generally a superset of \ASCII. - -\strong{Future compatibility note:} It may be tempting to assume that the -character set for 8-bit characters is ISO Latin-1 (an \ASCII{} -superset that covers most western languages that use the Latin -alphabet), but it is possible that in the future Unicode text editors -will become common. These generally use the UTF-8 encoding, which is -also an \ASCII{} superset, but with very different use for the -characters with ordinals 128-255. While there is no consensus on this -subject yet, it is unwise to assume either Latin-1 or UTF-8, even -though the current implementation appears to favor Latin-1. This -applies both to the source character set and the run-time character -set. - - -\section{Line structure\label{line-structure}} - -A Python program is divided into a number of \emph{logical lines}. -\index{line structure} - - -\subsection{Logical lines\label{logical}} - -The end of -a logical line is represented by the token NEWLINE. Statements cannot -cross logical line boundaries except where NEWLINE is allowed by the -syntax (e.g., between statements in compound statements). -A logical line is constructed from one or more \emph{physical lines} -by following the explicit or implicit \emph{line joining} rules. -\index{logical line} -\index{physical line} -\index{line joining} -\index{NEWLINE token} - - -\subsection{Physical lines\label{physical}} - -A physical line is a sequence of characters terminated by an end-of-line -sequence. In source files, any of the standard platform line -termination sequences can be used - the \UNIX{} form using \ASCII{} LF -(linefeed), the Windows form using the \ASCII{} sequence CR LF (return -followed by linefeed), or the Macintosh form using the \ASCII{} CR -(return) character. All of these forms can be used equally, regardless -of platform. - -When embedding Python, source code strings should be passed to Python -APIs using the standard C conventions for newline characters (the -\code{\e n} character, representing \ASCII{} LF, is the line -terminator). - - -\subsection{Comments\label{comments}} - -A comment starts with a hash character (\code{\#}) that is not part of -a string literal, and ends at the end of the physical line. A comment -signifies the end of the logical line unless the implicit line joining -rules are invoked. -Comments are ignored by the syntax; they are not tokens. -\index{comment} -\index{hash character} - - -\subsection{Encoding declarations\label{encodings}} -\index{source character set} -\index{encodings} - -If a comment in the first or second line of the Python script matches -the regular expression \regexp{coding[=:]\e s*([-\e w.]+)}, this comment is -processed as an encoding declaration; the first group of this -expression names the encoding of the source code file. The recommended -forms of this expression are - -\begin{verbatim} -# -*- coding: <encoding-name> -*- -\end{verbatim} - -which is recognized also by GNU Emacs, and - -\begin{verbatim} -# vim:fileencoding=<encoding-name> -\end{verbatim} - -which is recognized by Bram Moolenaar's VIM. In addition, if the first -bytes of the file are the UTF-8 byte-order mark -(\code{'\e xef\e xbb\e xbf'}), the declared file encoding is UTF-8 -(this is supported, among others, by Microsoft's \program{notepad}). - -If an encoding is declared, the encoding name must be recognized by -Python. % XXX there should be a list of supported encodings. -The encoding is used for all lexical analysis, in particular to find -the end of a string, and to interpret the contents of Unicode literals. -String literals are converted to Unicode for syntactical analysis, -then converted back to their original encoding before interpretation -starts. The encoding declaration must appear on a line of its own. - -\subsection{Explicit line joining\label{explicit-joining}} - -Two or more physical lines may be joined into logical lines using -backslash characters (\code{\e}), as follows: when a physical line ends -in a backslash that is not part of a string literal or comment, it is -joined with the following forming a single logical line, deleting the -backslash and the following end-of-line character. For example: -\index{physical line} -\index{line joining} -\index{line continuation} -\index{backslash character} -% -\begin{verbatim} -if 1900 < year < 2100 and 1 <= month <= 12 \ - and 1 <= day <= 31 and 0 <= hour < 24 \ - and 0 <= minute < 60 and 0 <= second < 60: # Looks like a valid date - return 1 -\end{verbatim} - -A line ending in a backslash cannot carry a comment. A backslash does -not continue a comment. A backslash does not continue a token except -for string literals (i.e., tokens other than string literals cannot be -split across physical lines using a backslash). A backslash is -illegal elsewhere on a line outside a string literal. - - -\subsection{Implicit line joining\label{implicit-joining}} - -Expressions in parentheses, square brackets or curly braces can be -split over more than one physical line without using backslashes. -For example: - -\begin{verbatim} -month_names = ['Januari', 'Februari', 'Maart', # These are the - 'April', 'Mei', 'Juni', # Dutch names - 'Juli', 'Augustus', 'September', # for the months - 'Oktober', 'November', 'December'] # of the year -\end{verbatim} - -Implicitly continued lines can carry comments. The indentation of the -continuation lines is not important. Blank continuation lines are -allowed. There is no NEWLINE token between implicit continuation -lines. Implicitly continued lines can also occur within triple-quoted -strings (see below); in that case they cannot carry comments. - - -\subsection{Blank lines \label{blank-lines}} - -\index{blank line} -A logical line that contains only spaces, tabs, formfeeds and possibly -a comment, is ignored (i.e., no NEWLINE token is generated). During -interactive input of statements, handling of a blank line may differ -depending on the implementation of the read-eval-print loop. In the -standard implementation, an entirely blank logical line (i.e.\ one -containing not even whitespace or a comment) terminates a multi-line -statement. - - -\subsection{Indentation\label{indentation}} - -Leading whitespace (spaces and tabs) at the beginning of a logical -line is used to compute the indentation level of the line, which in -turn is used to determine the grouping of statements. -\index{indentation} -\index{whitespace} -\index{leading whitespace} -\index{space} -\index{tab} -\index{grouping} -\index{statement grouping} - -First, tabs are replaced (from left to right) by one to eight spaces -such that the total number of characters up to and including the -replacement is a multiple of -eight (this is intended to be the same rule as used by \UNIX). The -total number of spaces preceding the first non-blank character then -determines the line's indentation. Indentation cannot be split over -multiple physical lines using backslashes; the whitespace up to the -first backslash determines the indentation. - -\strong{Cross-platform compatibility note:} because of the nature of -text editors on non-UNIX platforms, it is unwise to use a mixture of -spaces and tabs for the indentation in a single source file. It -should also be noted that different platforms may explicitly limit the -maximum indentation level. - -A formfeed character may be present at the start of the line; it will -be ignored for the indentation calculations above. Formfeed -characters occurring elsewhere in the leading whitespace have an -undefined effect (for instance, they may reset the space count to -zero). - -The indentation levels of consecutive lines are used to generate -INDENT and DEDENT tokens, using a stack, as follows. -\index{INDENT token} -\index{DEDENT token} - -Before the first line of the file is read, a single zero is pushed on -the stack; this will never be popped off again. The numbers pushed on -the stack will always be strictly increasing from bottom to top. At -the beginning of each logical line, the line's indentation level is -compared to the top of the stack. If it is equal, nothing happens. -If it is larger, it is pushed on the stack, and one INDENT token is -generated. If it is smaller, it \emph{must} be one of the numbers -occurring on the stack; all numbers on the stack that are larger are -popped off, and for each number popped off a DEDENT token is -generated. At the end of the file, a DEDENT token is generated for -each number remaining on the stack that is larger than zero. - -Here is an example of a correctly (though confusingly) indented piece -of Python code: - -\begin{verbatim} -def perm(l): - # Compute the list of all permutations of l - if len(l) <= 1: - return [l] - r = [] - for i in range(len(l)): - s = l[:i] + l[i+1:] - p = perm(s) - for x in p: - r.append(l[i:i+1] + x) - return r -\end{verbatim} - -The following example shows various indentation errors: - -\begin{verbatim} - def perm(l): # error: first line indented -for i in range(len(l)): # error: not indented - s = l[:i] + l[i+1:] - p = perm(l[:i] + l[i+1:]) # error: unexpected indent - for x in p: - r.append(l[i:i+1] + x) - return r # error: inconsistent dedent -\end{verbatim} - -(Actually, the first three errors are detected by the parser; only the -last error is found by the lexical analyzer --- the indentation of -\code{return r} does not match a level popped off the stack.) - - -\subsection{Whitespace between tokens\label{whitespace}} - -Except at the beginning of a logical line or in string literals, the -whitespace characters space, tab and formfeed can be used -interchangeably to separate tokens. Whitespace is needed between two -tokens only if their concatenation could otherwise be interpreted as a -different token (e.g., ab is one token, but a b is two tokens). - - -\section{Other tokens\label{other-tokens}} - -Besides NEWLINE, INDENT and DEDENT, the following categories of tokens -exist: \emph{identifiers}, \emph{keywords}, \emph{literals}, -\emph{operators}, and \emph{delimiters}. -Whitespace characters (other than line terminators, discussed earlier) -are not tokens, but serve to delimit tokens. -Where -ambiguity exists, a token comprises the longest possible string that -forms a legal token, when read from left to right. - - -\section{Identifiers and keywords\label{identifiers}} - -Identifiers (also referred to as \emph{names}) are described by the following -lexical definitions: -\index{identifier} -\index{name} - -\begin{productionlist} - \production{identifier} - {(\token{letter}|"_") (\token{letter} | \token{digit} | "_")*} - \production{letter} - {\token{lowercase} | \token{uppercase}} - \production{lowercase} - {"a"..."z"} - \production{uppercase} - {"A"..."Z"} - \production{digit} - {"0"..."9"} -\end{productionlist} - -Identifiers are unlimited in length. Case is significant. - - -\subsection{Keywords\label{keywords}} - -The following identifiers are used as reserved words, or -\emph{keywords} of the language, and cannot be used as ordinary -identifiers. They must be spelled exactly as written here:% -\index{keyword}% -\index{reserved word} - -\begin{verbatim} -and del from not while -as elif global or with -assert else if pass yield -break except import print -class exec in raise -continue finally is return -def for lambda try -\end{verbatim} - -% When adding keywords, use reswords.py for reformatting - -\versionchanged[\constant{None} became a constant and is now -recognized by the compiler as a name for the built-in object -\constant{None}. Although it is not a keyword, you cannot assign -a different object to it]{2.4} - -\versionchanged[Both \keyword{as} and \keyword{with} are only recognized -when the \code{with_statement} future feature has been enabled. -It will always be enabled in Python 2.6. See section~\ref{with} for -details. Note that using \keyword{as} and \keyword{with} as identifiers -will always issue a warning, even when the \code{with_statement} future -directive is not in effect]{2.5} - - -\subsection{Reserved classes of identifiers\label{id-classes}} - -Certain classes of identifiers (besides keywords) have special -meanings. These classes are identified by the patterns of leading and -trailing underscore characters: - -\begin{description} - -\item[\code{_*}] - Not imported by \samp{from \var{module} import *}. The special - identifier \samp{_} is used in the interactive interpreter to store - the result of the last evaluation; it is stored in the - \module{__builtin__} module. When not in interactive mode, \samp{_} - has no special meaning and is not defined. - See section~\ref{import}, ``The \keyword{import} statement.'' - - \note{The name \samp{_} is often used in conjunction with - internationalization; refer to the documentation for the - \ulink{\module{gettext} module}{../lib/module-gettext.html} for more - information on this convention.} - -\item[\code{__*__}] - System-defined names. These names are defined by the interpreter - and its implementation (including the standard library); - applications should not expect to define additional names using this - convention. The set of names of this class defined by Python may be - extended in future versions. - See section~\ref{specialnames}, ``Special method names.'' - -\item[\code{__*}] - Class-private names. Names in this category, when used within the - context of a class definition, are re-written to use a mangled form - to help avoid name clashes between ``private'' attributes of base - and derived classes. - See section~\ref{atom-identifiers}, ``Identifiers (Names).'' - -\end{description} - - -\section{Literals\label{literals}} - -Literals are notations for constant values of some built-in types. -\index{literal} -\index{constant} - - -\subsection{String literals\label{strings}} - -String literals are described by the following lexical definitions: -\index{string literal} - -\index{ASCII@\ASCII} -\begin{productionlist} - \production{stringliteral} - {[\token{stringprefix}](\token{shortstring} | \token{longstring})} - \production{stringprefix} - {"r" | "u" | "ur" | "R" | "U" | "UR" | "Ur" | "uR"} - \production{shortstring} - {"'" \token{shortstringitem}* "'" - | '"' \token{shortstringitem}* '"'} - \production{longstring} - {"'''" \token{longstringitem}* "'''"} - \productioncont{| '"""' \token{longstringitem}* '"""'} - \production{shortstringitem} - {\token{shortstringchar} | \token{escapeseq}} - \production{longstringitem} - {\token{longstringchar} | \token{escapeseq}} - \production{shortstringchar} - {<any source character except "\e" or newline or the quote>} - \production{longstringchar} - {<any source character except "\e">} - \production{escapeseq} - {"\e" <any ASCII character>} -\end{productionlist} - -One syntactic restriction not indicated by these productions is that -whitespace is not allowed between the \grammartoken{stringprefix} and -the rest of the string literal. The source character set is defined -by the encoding declaration; it is \ASCII{} if no encoding declaration -is given in the source file; see section~\ref{encodings}. - -\index{triple-quoted string} -\index{Unicode Consortium} -\index{string!Unicode} -In plain English: String literals can be enclosed in matching single -quotes (\code{'}) or double quotes (\code{"}). They can also be -enclosed in matching groups of three single or double quotes (these -are generally referred to as \emph{triple-quoted strings}). The -backslash (\code{\e}) character is used to escape characters that -otherwise have a special meaning, such as newline, backslash itself, -or the quote character. String literals may optionally be prefixed -with a letter \character{r} or \character{R}; such strings are called -\dfn{raw strings}\index{raw string} and use different rules for interpreting -backslash escape sequences. A prefix of \character{u} or \character{U} -makes the string a Unicode string. Unicode strings use the Unicode character -set as defined by the Unicode Consortium and ISO~10646. Some additional -escape sequences, described below, are available in Unicode strings. -The two prefix characters may be combined; in this case, \character{u} must -appear before \character{r}. - -In triple-quoted strings, -unescaped newlines and quotes are allowed (and are retained), except -that three unescaped quotes in a row terminate the string. (A -``quote'' is the character used to open the string, i.e. either -\code{'} or \code{"}.) - -Unless an \character{r} or \character{R} prefix is present, escape -sequences in strings are interpreted according to rules similar -to those used by Standard C. The recognized escape sequences are: -\index{physical line} -\index{escape sequence} -\index{Standard C} -\index{C} - -\begin{tableiii}{l|l|c}{code}{Escape Sequence}{Meaning}{Notes} -\lineiii{\e\var{newline}} {Ignored}{} -\lineiii{\e\e} {Backslash (\code{\e})}{} -\lineiii{\e'} {Single quote (\code{'})}{} -\lineiii{\e"} {Double quote (\code{"})}{} -\lineiii{\e a} {\ASCII{} Bell (BEL)}{} -\lineiii{\e b} {\ASCII{} Backspace (BS)}{} -\lineiii{\e f} {\ASCII{} Formfeed (FF)}{} -\lineiii{\e n} {\ASCII{} Linefeed (LF)}{} -\lineiii{\e N\{\var{name}\}} - {Character named \var{name} in the Unicode database (Unicode only)}{} -\lineiii{\e r} {\ASCII{} Carriage Return (CR)}{} -\lineiii{\e t} {\ASCII{} Horizontal Tab (TAB)}{} -\lineiii{\e u\var{xxxx}} - {Character with 16-bit hex value \var{xxxx} (Unicode only)}{(1)} -\lineiii{\e U\var{xxxxxxxx}} - {Character with 32-bit hex value \var{xxxxxxxx} (Unicode only)}{(2)} -\lineiii{\e v} {\ASCII{} Vertical Tab (VT)}{} -\lineiii{\e\var{ooo}} {Character with octal value \var{ooo}}{(3,5)} -\lineiii{\e x\var{hh}} {Character with hex value \var{hh}}{(4,5)} -\end{tableiii} -\index{ASCII@\ASCII} - -\noindent -Notes: - -\begin{itemize} -\item[(1)] - Individual code units which form parts of a surrogate pair can be - encoded using this escape sequence. -\item[(2)] - Any Unicode character can be encoded this way, but characters - outside the Basic Multilingual Plane (BMP) will be encoded using a - surrogate pair if Python is compiled to use 16-bit code units (the - default). Individual code units which form parts of a surrogate - pair can be encoded using this escape sequence. -\item[(3)] - As in Standard C, up to three octal digits are accepted. -\item[(4)] - Unlike in Standard C, at most two hex digits are accepted. -\item[(5)] - In a string literal, hexadecimal and octal escapes denote the - byte with the given value; it is not necessary that the byte - encodes a character in the source character set. In a Unicode - literal, these escapes denote a Unicode character with the given - value. -\end{itemize} - - -Unlike Standard \index{unrecognized escape sequence}C, -all unrecognized escape sequences are left in the string unchanged, -i.e., \emph{the backslash is left in the string}. (This behavior is -useful when debugging: if an escape sequence is mistyped, the -resulting output is more easily recognized as broken.) It is also -important to note that the escape sequences marked as ``(Unicode -only)'' in the table above fall into the category of unrecognized -escapes for non-Unicode string literals. - -When an \character{r} or \character{R} prefix is present, a character -following a backslash is included in the string without change, and \emph{all -backslashes are left in the string}. For example, the string literal -\code{r"\e n"} consists of two characters: a backslash and a lowercase -\character{n}. String quotes can be escaped with a backslash, but the -backslash remains in the string; for example, \code{r"\e""} is a valid string -literal consisting of two characters: a backslash and a double quote; -\code{r"\e"} is not a valid string literal (even a raw string cannot -end in an odd number of backslashes). Specifically, \emph{a raw -string cannot end in a single backslash} (since the backslash would -escape the following quote character). Note also that a single -backslash followed by a newline is interpreted as those two characters -as part of the string, \emph{not} as a line continuation. - -When an \character{r} or \character{R} prefix is used in conjunction -with a \character{u} or \character{U} prefix, then the \code{\e uXXXX} -and \code{\e UXXXXXXXX} escape sequences are processed while -\emph{all other backslashes are left in the string}. -For example, the string literal -\code{ur"\e{}u0062\e n"} consists of three Unicode characters: `LATIN -SMALL LETTER B', `REVERSE SOLIDUS', and `LATIN SMALL LETTER N'. -Backslashes can be escaped with a preceding backslash; however, both -remain in the string. As a result, \code{\e uXXXX} escape sequences -are only recognized when there are an odd number of backslashes. - -\subsection{String literal concatenation\label{string-catenation}} - -Multiple adjacent string literals (delimited by whitespace), possibly -using different quoting conventions, are allowed, and their meaning is -the same as their concatenation. Thus, \code{"hello" 'world'} is -equivalent to \code{"helloworld"}. This feature can be used to reduce -the number of backslashes needed, to split long strings conveniently -across long lines, or even to add comments to parts of strings, for -example: - -\begin{verbatim} -re.compile("[A-Za-z_]" # letter or underscore - "[A-Za-z0-9_]*" # letter, digit or underscore - ) -\end{verbatim} - -Note that this feature is defined at the syntactical level, but -implemented at compile time. The `+' operator must be used to -concatenate string expressions at run time. Also note that literal -concatenation can use different quoting styles for each component -(even mixing raw strings and triple quoted strings). - - -\subsection{Numeric literals\label{numbers}} - -There are four types of numeric literals: plain integers, long -integers, floating point numbers, and imaginary numbers. There are no -complex literals (complex numbers can be formed by adding a real -number and an imaginary number). -\index{number} -\index{numeric literal} -\index{integer literal} -\index{plain integer literal} -\index{long integer literal} -\index{floating point literal} -\index{hexadecimal literal} -\index{octal literal} -\index{decimal literal} -\index{imaginary literal} -\index{complex!literal} - -Note that numeric literals do not include a sign; a phrase like -\code{-1} is actually an expression composed of the unary operator -`\code{-}' and the literal \code{1}. - - -\subsection{Integer and long integer literals\label{integers}} - -Integer and long integer literals are described by the following -lexical definitions: - -\begin{productionlist} - \production{longinteger} - {\token{integer} ("l" | "L")} - \production{integer} - {\token{decimalinteger} | \token{octinteger} | \token{hexinteger}} - \production{decimalinteger} - {\token{nonzerodigit} \token{digit}* | "0"} - \production{octinteger} - {"0" \token{octdigit}+} - \production{hexinteger} - {"0" ("x" | "X") \token{hexdigit}+} - \production{nonzerodigit} - {"1"..."9"} - \production{octdigit} - {"0"..."7"} - \production{hexdigit} - {\token{digit} | "a"..."f" | "A"..."F"} -\end{productionlist} - -Although both lower case \character{l} and upper case \character{L} are -allowed as suffix for long integers, it is strongly recommended to always -use \character{L}, since the letter \character{l} looks too much like the -digit \character{1}. - -Plain integer literals that are above the largest representable plain -integer (e.g., 2147483647 when using 32-bit arithmetic) are accepted -as if they were long integers instead.\footnote{In versions of Python -prior to 2.4, octal and hexadecimal literals in the range just above -the largest representable plain integer but below the largest unsigned -32-bit number (on a machine using 32-bit arithmetic), 4294967296, were -taken as the negative plain integer obtained by subtracting 4294967296 -from their unsigned value.} There is no limit for long integer -literals apart from what can be stored in available memory. - -Some examples of plain integer literals (first row) and long integer -literals (second and third rows): - -\begin{verbatim} -7 2147483647 0177 -3L 79228162514264337593543950336L 0377L 0x100000000L - 79228162514264337593543950336 0xdeadbeef -\end{verbatim} - - -\subsection{Floating point literals\label{floating}} - -Floating point literals are described by the following lexical -definitions: - -\begin{productionlist} - \production{floatnumber} - {\token{pointfloat} | \token{exponentfloat}} - \production{pointfloat} - {[\token{intpart}] \token{fraction} | \token{intpart} "."} - \production{exponentfloat} - {(\token{intpart} | \token{pointfloat}) - \token{exponent}} - \production{intpart} - {\token{digit}+} - \production{fraction} - {"." \token{digit}+} - \production{exponent} - {("e" | "E") ["+" | "-"] \token{digit}+} -\end{productionlist} - -Note that the integer and exponent parts of floating point numbers -can look like octal integers, but are interpreted using radix 10. For -example, \samp{077e010} is legal, and denotes the same number -as \samp{77e10}. -The allowed range of floating point literals is -implementation-dependent. -Some examples of floating point literals: - -\begin{verbatim} -3.14 10. .001 1e100 3.14e-10 0e0 -\end{verbatim} - -Note that numeric literals do not include a sign; a phrase like -\code{-1} is actually an expression composed of the unary operator -\code{-} and the literal \code{1}. - - -\subsection{Imaginary literals\label{imaginary}} - -Imaginary literals are described by the following lexical definitions: - -\begin{productionlist} - \production{imagnumber}{(\token{floatnumber} | \token{intpart}) ("j" | "J")} -\end{productionlist} - -An imaginary literal yields a complex number with a real part of -0.0. Complex numbers are represented as a pair of floating point -numbers and have the same restrictions on their range. To create a -complex number with a nonzero real part, add a floating point number -to it, e.g., \code{(3+4j)}. Some examples of imaginary literals: - -\begin{verbatim} -3.14j 10.j 10j .001j 1e100j 3.14e-10j -\end{verbatim} - - -\section{Operators\label{operators}} - -The following tokens are operators: -\index{operators} - -\begin{verbatim} -+ - * ** / // % -<< >> & | ^ ~ -< > <= >= == != <> -\end{verbatim} - -The comparison operators \code{<>} and \code{!=} are alternate -spellings of the same operator. \code{!=} is the preferred spelling; -\code{<>} is obsolescent. - - -\section{Delimiters\label{delimiters}} - -The following tokens serve as delimiters in the grammar: -\index{delimiters} - -\begin{verbatim} -( ) [ ] { } @ -, : . ` = ; -+= -= *= /= //= %= -&= |= ^= >>= <<= **= -\end{verbatim} - -The period can also occur in floating-point and imaginary literals. A -sequence of three periods has a special meaning as an ellipsis in slices. -The second half of the list, the augmented assignment operators, serve -lexically as delimiters, but also perform an operation. - -The following printing \ASCII{} characters have special meaning as part -of other tokens or are otherwise significant to the lexical analyzer: - -\begin{verbatim} -' " # \ -\end{verbatim} - -The following printing \ASCII{} characters are not used in Python. Their -occurrence outside string literals and comments is an unconditional -error: -\index{ASCII@\ASCII} - -\begin{verbatim} -$ ? -\end{verbatim} |