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diff --git a/doc/tut.tex b/doc/tut.tex index ad5f56c..e0229b9 100644 --- a/doc/tut.tex +++ b/doc/tut.tex @@ -9,10 +9,10 @@ } \author{ - Guido van Rossum \\ - Dept. CST, CWI, Kruislaan 413 \\ - 1098 SJ Amsterdam, The Netherlands \\ - E-mail: {\tt [email protected]} + Guido van Rossum \\ + Dept. CST, CWI, Kruislaan 413 \\ + 1098 SJ Amsterdam, The Netherlands \\ + E-mail: {\tt [email protected]} } \begin{document} @@ -154,15 +154,15 @@ installation option, other places instead of are possible; check with your local \Python\ guru or system administrator.% \footnote{ - At CWI, at the time of writing, the interpreter can be found in - the following places: - On the Amoeba Ultrix machines, use the standard path, - {\tt /usr/local/python}. - On the Sun file servers, use - {\tt /ufs/guido/bin/}{\em arch}{\tt /python}, - where {\em arch} can be {\tt sgi} or {\tt sun4}. - On piring, use {\tt /userfs3/amoeba/bin/python}. - (If you can't find a binary advertised here, get in touch with me.) + At CWI, at the time of writing, the interpreter can be found in + the following places: + On the Amoeba Ultrix machines, use the standard path, + {\tt /usr/local/python}. + On the Sun file servers, use + {\tt /ufs/guido/bin/}{\em arch}{\tt /python}, + where {\em arch} can be {\tt sgi} or {\tt sun4}. + On piring, use {\tt /userfs3/amoeba/bin/python}. + (If you can't find a binary advertised here, get in touch with me.) } The interpreter operates somewhat like the \UNIX\ shell: when called with @@ -172,13 +172,13 @@ standard input, it reads and executes a {\em script} from that file.% \footnote{ - There is a difference between ``{\tt python file}'' and - ``{\tt python $<$file}''. In the latter case {\tt input()} and - {\tt raw\_input()} are satisfied from {\em file}, which has - already been read until the end by the parser, so they will read - EOF immediately. In the former case (which is usually what - you want) they are satisfied from whatever file or device is - connected to standard input of the \Python\ interpreter. + There is a difference between ``{\tt python file}'' and + ``{\tt python $<$file}''. In the latter case {\tt input()} and + {\tt raw\_input()} are satisfied from {\em file}, which has + already been read until the end by the parser, so they will read + EOF immediately. In the former case (which is usually what + you want) they are satisfied from whatever file or device is + connected to standard input of the \Python\ interpreter. } If available, the script name and additional arguments thereafter are passed to the script in the variable @@ -232,10 +232,10 @@ When is not set, an installation-dependent default path is used, usually {\tt .:/usr/local/lib/python}.% \footnote{ - Modules are really searched in the list of directories given by - the variable {\tt sys.path} which is initialized from - {\tt PYTHONPATH} or from the installation-dependent default. - See the section on Standard Modules later. + Modules are really searched in the list of directories given by + the variable {\tt sys.path} which is initialized from + {\tt PYTHONPATH} or from the installation-dependent default. + See the section on Standard Modules later. } On BSD'ish \UNIX\ systems, \Python\ scripts can be made directly executable, @@ -262,10 +262,10 @@ however, the basics are easily explained. If supported,% \footnote{ - Perhaps the quickest check to see whether command line editing - is supported is typing Control-P to the first \Python\ prompt - you get. If it beeps, you have command line editing. - If not, you can skip the rest of this section. + Perhaps the quickest check to see whether command line editing + is supported is typing Control-P to the first \Python\ prompt + you get. If it beeps, you have command line editing. + If not, you can skip the rest of this section. } input line editing is active whenever the interpreter prints a primary or secondary prompt. @@ -423,9 +423,9 @@ notation: two subscripts (indices) separated by a colon. >>> word[2:4] 'lp' >>> # Slice indices have useful defaults: ->>> word[:2] # Take first two characters +>>> word[:2] # Take first two characters 'He' ->>> word[2:] # Drop first two characters +>>> word[2:] # Drop first two characters 'lpA' >>> # A useful invariant: s[:i] + s[i:] = s >>> word[:3] + word[3:] @@ -448,12 +448,12 @@ Slice indices (but not simple subscripts) may be negative numbers, to start counting from the right. For example: \bcode\begin{verbatim} ->>> word[-2:] # Take last two characters +>>> word[-2:] # Take last two characters 'pA' ->>> word[:-2] # Drop last two characters +>>> word[:-2] # Drop last two characters 'Hel' >>> # But -0 does not count from the right! ->>> word[-0:] # (since -0 equals 0) +>>> word[-0:] # (since -0 equals 0) 'HelpA' >>> \end{verbatim}\ecode @@ -470,8 +470,8 @@ for example: +---+---+---+---+---+ | H | e | l | p | A | +---+---+---+---+---+ - 0 1 2 3 4 5 --5 -4 -3 -2 -1 + 0 1 2 3 4 5 +-5 -4 -3 -2 -1 \end{verbatim}\ecode The first row of numbers gives the position of the indices 0...5 in the string; the second row gives the corresponding negative indices. @@ -570,8 +570,8 @@ series as follows: >>> # the sum of two elements defines the next >>> a, b = 0, 1 >>> while b < 100: -... print b -... a, b = b, a+b +... print b +... a, b = b, a+b ... 1 1 @@ -616,9 +616,9 @@ The standard comparison operators are written as and {\tt <>}.% \footnote{ - The ambiguity of using {\tt =} - for both assignment and equality is resolved by disallowing - unparenthesized conditions at the right hand side of assignments. + The ambiguity of using {\tt =} + for both assignment and equality is resolved by disallowing + unparenthesized conditions at the right hand side of assignments. } \item The @@ -651,8 +651,8 @@ A trailing comma avoids the newline after the output: \bcode\begin{verbatim} >>> a, b = 0, 1 >>> while b < 1000: -... print b, -... a, b = b, a+b +... print b, +... a, b = b, a+b ... 1 1 2 3 5 8 13 21 34 55 89 144 233 377 610 987 >>> @@ -673,14 +673,14 @@ Perhaps the most well-known statement type is the {\tt if} statement. For example: \bcode\begin{verbatim} >>> if x < 0: -... x = 0 -... print 'Negative changed to zero' +... x = 0 +... print 'Negative changed to zero' ... elif x = 0: -... print 'Zero' +... print 'Zero' ... elif x = 1: -... print 'Single' +... print 'Single' ... else: -... print 'More' +... print 'More' ... \end{verbatim}\ecode There can be zero or more {\tt elif} parts, and the {\tt else} part is @@ -703,7 +703,7 @@ For example (no pun intended): >>> # Measure some strings: >>> a = ['cat', 'window', 'defenestrate'] >>> for x in a: -... print x, len(x) +... print x, len(x) ... cat 3 window 6 @@ -741,7 +741,7 @@ and {\tt len()} as follows: \bcode\begin{verbatim} >>> a = ['Mary', 'had', 'a', 'little', 'boy'] >>> for i in range(len(a)): -... print i, a[i] +... print i, a[i] ... 0 Mary 1 had @@ -763,12 +763,12 @@ This is exemplified by the following loop, which searches for a list item of value 0: \bcode\begin{verbatim} >>> for n in range(2, 10): -... for x in range(2, n): -... if n % x = 0: -... print n, 'equals', x, '*', n/x -... break -... else: -... print n, 'is a prime number' +... for x in range(2, n): +... if n % x = 0: +... print n, 'equals', x, '*', n/x +... break +... else: +... print n, 'is a prime number' ... 2 is a prime number 3 is a prime number @@ -789,7 +789,7 @@ program requires no action. For example: \bcode\begin{verbatim} >>> while 1: -... pass # Busy-wait for keyboard interrupt +... pass # Busy-wait for keyboard interrupt ... \end{verbatim}\ecode @@ -802,11 +802,11 @@ XXX To Be Done. We can create a function that writes the Fibonacci series to an arbitrary boundary: \bcode\begin{verbatim} ->>> def fib(n): # write Fibonacci series up to n -... a, b = 0, 1 -... while b <= n: -... print b, -... a, b = b, a+b +>>> def fib(n): # write Fibonacci series up to n +... a, b = 0, 1 +... while b <= n: +... print b, +... a, b = b, a+b ... >>> # Now call the function we just defined: >>> fib(2000) @@ -837,10 +837,10 @@ the local symbol table of the called function when it is called; thus, arguments are passed using {\em call\ by\ value}.% \footnote{ - Actually, {\em call by object reference} would be a better - description, since if a mutable object is passed, the caller - will see any changes the callee makes to it (e.g., items - inserted into a list). + Actually, {\em call by object reference} would be a better + description, since if a mutable object is passed, the caller + will see any changes the callee makes to it (e.g., items + inserted into a list). } When a function calls another function, a new local symbol table is created for that call. @@ -880,15 +880,15 @@ It is simple to write a function that returns a list of the numbers of the Fibonacci series, instead of printing it: \bcode\begin{verbatim} >>> def fib2(n): # return Fibonacci series up to n -... result = [] -... a, b = 0, 1 -... while b <= n: -... result.append(b) # see below -... a, b = b, a+b -... return result +... result = [] +... a, b = 0, 1 +... while b <= n: +... result.append(b) # see below +... a, b = b, a+b +... return result ... ->>> f100 = fib2(100) # call it ->>> f100 # write the result +>>> f100 = fib2(100) # call it +>>> f100 # write the result [1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89] >>> \end{verbatim}\ecode @@ -928,8 +928,8 @@ In this case it is equivalent to {\tt ret = ret + [b]}, but more efficient.% \footnote{ - There is a subtle semantic difference if the object - is referenced from more than one place. + There is a subtle semantic difference if the object + is referenced from more than one place. } \end{itemize} The list object type has two more methods: @@ -993,19 +993,19 @@ in the current directory with the following contents: \bcode\begin{verbatim} # Fibonacci numbers module -def fib(n): # write Fibonacci series up to n - a, b = 0, 1 - while b <= n: - print b, - a, b = b, a+b +def fib(n): # write Fibonacci series up to n + a, b = 0, 1 + while b <= n: + print b, + a, b = b, a+b def fib2(n): # return Fibonacci series up to n - ret = [] - a, b = 0, 1 - while b <= n: - ret.append(b) - a, b = b, a+b - return ret + ret = [] + a, b = 0, 1 + while b <= n: + ret.append(b) + a, b = b, a+b + return ret \end{verbatim}\ecode Now enter the \Python\ interpreter and import this module with the following command: @@ -1043,9 +1043,9 @@ They are executed only the {\em first} time the module is imported somewhere.% \footnote{ - In fact function definitions are also `statements' that are - `executed'; the execution enters the function name in the - module's global symbol table. + In fact function definitions are also `statements' that are + `executed'; the execution enters the function name in the + module's global symbol table. } Each module has its own private symbol table, which is used as the @@ -1157,7 +1157,7 @@ kind of complaint you get while you are still learning \Python: >>> while 1 print 'Hello world' Parsing error: file <stdin>, line 1: while 1 print 'Hello world' - ^ + ^ Unhandled exception: run-time error: syntax error >>> \end{verbatim}\ecode @@ -1178,15 +1178,15 @@ an error when an attempt is made to execute it: >>> 10 * (1/0) Unhandled exception: run-time error: integer division by zero Stack backtrace (innermost last): - File "<stdin>", line 1 + File "<stdin>", line 1 >>> 4 + foo*3 Unhandled exception: undefined name: foo Stack backtrace (innermost last): - File "<stdin>", line 1 + File "<stdin>", line 1 >>> '2' + 2 Unhandled exception: type error: illegal argument type for built-in operation Stack backtrace (innermost last): - File "<stdin>", line 1 + File "<stdin>", line 1 >>> \end{verbatim}\ecode Errors detected during execution are called @@ -1223,9 +1223,9 @@ The detail states the cause of the error in more detail. errors are more serious: these are usually caused by misspelled identifiers.% \footnote{ - The parser does not check whether names used in a program are at - all defined elsewhere in the program, so such checks are - postponed until run-time. The same holds for type checking. + The parser does not check whether names used in a program are at + all defined elsewhere in the program, so such checks are + postponed until run-time. The same holds for type checking. } The detail is the offending identifier. \item @@ -1244,11 +1244,11 @@ some floating point numbers: \bcode\begin{verbatim} >>> numbers = [0.3333, 2.5, 0.0, 10.0] >>> for x in numbers: -... print x, -... try: -... print 1.0 / x -... except RuntimeError: -... print '*** has no inverse ***' +... print x, +... try: +... print 1.0 / x +... except RuntimeError: +... print '*** has no inverse ***' ... 0.3333 3.00030003 2.5 0.4 @@ -1288,7 +1288,7 @@ An except clause may name multiple exceptions as a parenthesized list, e.g.: \bcode\begin{verbatim} ... except (RuntimeError, TypeError, NameError): -... pass +... pass \end{verbatim}\ecode The last except clause may omit the exception name(s), to serve as a wildcard. @@ -1303,9 +1303,9 @@ specify a variable after the exception name (or list) to receive the argument's value, as follows: \bcode\begin{verbatim} >>> try: -... foo() +... foo() ... except NameError, x: -... print 'name', x, 'undefined' +... print 'name', x, 'undefined' ... name foo undefined >>> @@ -1319,21 +1319,21 @@ These are in fact string objects whose {\em object\ identity} (not their value!) identifies the exceptions.% \footnote{ - There should really be a separate exception type; it is pure - laziness that exceptions are identified by strings, and this may - be fixed in the future. + There should really be a separate exception type; it is pure + laziness that exceptions are identified by strings, and this may + be fixed in the future. } The string is printed as the second part of the message for unhandled exceptions. Their names and values are: \bcode\begin{verbatim} -EOFError 'end-of-file read' -KeyboardInterrupt 'keyboard interrupt' -MemoryError 'out of memory' * -NameError 'undefined name' * -RuntimeError 'run-time error' * -SystemError 'system error' * -TypeError 'type error' * +EOFError 'end-of-file read' +KeyboardInterrupt 'keyboard interrupt' +MemoryError 'out of memory' * +NameError 'undefined name' * +RuntimeError 'run-time error' * +SystemError 'system error' * +TypeError 'type error' * \end{verbatim}\ecode The meanings should be clear enough. Those exceptions with a {\tt *} in the third column have an argument. @@ -1344,12 +1344,12 @@ that are called (even indirectly) in the try clause. For example: \bcode\begin{verbatim} >>> def this_fails(): -... x = 1/0 +... x = 1/0 ... >>> try: -... this_fails() +... this_fails() ... except RuntimeError, detail: -... print 'Handling run-time error:', detail +... print 'Handling run-time error:', detail ... Handling run-time error: domain error or zero division >>> @@ -1364,7 +1364,7 @@ For example: >>> raise NameError, 'Hi There!' Unhandled exception: undefined name: Hi There! Stack backtrace (innermost last): - File "<stdin>", line 1 + File "<stdin>", line 1 >>> \end{verbatim}\ecode The first argument to {\tt raise} names the exception to be raised. @@ -1378,15 +1378,15 @@ For example: \bcode\begin{verbatim} >>> my_exc = 'nobody likes me!' >>> try: -... raise my_exc, 2*2 +... raise my_exc, 2*2 ... except my_exc, val: -... print 'My exception occured, value:', val +... print 'My exception occured, value:', val ... My exception occured, value: 4 >>> raise my_exc, 1 Unhandled exception: nobody likes me!: 1 Stack backtrace (innermost last): - File "<stdin>", line 7 + File "<stdin>", line 7 >>> \end{verbatim}\ecode Many standard modules use this to report errors that may occur in @@ -1399,14 +1399,14 @@ define clean-up actions that must be executed under all circumstances. For example: \bcode\begin{verbatim} >>> try: -... raise KeyboardInterrupt +... raise KeyboardInterrupt ... finally: -... print 'Goodbye, world!' +... print 'Goodbye, world!' ... Goodbye, world! Unhandled exception: keyboard interrupt Stack backtrace (innermost last): - File "<stdin>", line 2 + File "<stdin>", line 2 >>> \end{verbatim}\ecode The @@ -1456,11 +1456,11 @@ Also, like Modula-3 but unlike C++, the built-in operators with special syntax (arithmetic operators, subscripting etc.) cannot be redefined for class members.% \footnote{ - They can be redefined for new object types implemented in C in - extensions to the interpreter, however. It would require only a - naming convention and a relatively small change to the - interpreter to allow operator overloading for classes, so - perhaps someday... + They can be redefined for new object types implemented in C in + extensions to the interpreter, however. It would require only a + naming convention and a relatively small change to the + interpreter to allow operator overloading for classes, so + perhaps someday... } \subsubsection{A Simple Example} @@ -1471,22 +1471,22 @@ remove elements, a membership test, and a request for the size of the set. \bcode\begin{verbatim} class Set(): - def new(self): - self.elements = [] - return self - def add(self, e): - if e not in self.elements: - self.elements.append(e) - def remove(self, e): - if e in self.elements: - for i in range(len(self.elements)): - if self.elements[i] = e: - del self.elements[i] - break - def is_element(self, e): - return e in self.elements - def size(self): - return len(self.elements) + def new(self): + self.elements = [] + return self + def add(self, e): + if e not in self.elements: + self.elements.append(e) + def remove(self, e): + if e in self.elements: + for i in range(len(self.elements)): + if self.elements[i] = e: + del self.elements[i] + break + def is_element(self, e): + return e in self.elements + def size(self): + return len(self.elements) \end{verbatim}\ecode Note that the class definition looks like a big compound statement, with all the function definitons indented repective to the @@ -1538,13 +1538,13 @@ XXX This section is not complete yet! \section{XXX P.M.} \begin{itemize} -\item The {\tt del} statement. -\item The {\tt dir()} function. -\item Tuples. -\item Dictionaries. -\item Objects and types in general. -\item Backquotes. -\item And/Or/Not. +\item The {\tt del} statement. +\item The {\tt dir()} function. +\item Tuples. +\item Dictionaries. +\item Objects and types in general. +\item Backquotes. +\item And/Or/Not. \end{itemize} \end{document} |