本文作者：
Patrick Jordan
Java 和 C 最流行的开发语言，计算机语言教学也大多围绕其展开，对于初学者来说Python语言可能会是一个更好的选择。
例子
BASIC,
C, Java 和 Python来做示例。
"Hello World" 程序测试两个方面：
- 花多少时间编写和调试
- 学习者在编写过程中需要理解的东西
BASIC
10 INPUT A
20 INPUT B
30 C=A+B
40 PRINT C
RUN
Time to write:
15 seconds. I admit I don't have a BASIC interpreter handy and did not
test this, but I just
know it works. (OK, I fired up the TRS-80
emulator and actually ran it - it works...)
Things to explain:
- Line numbers
- Variables
- INPUT
- PRINT
- RUN
Pros and Cons
BASIC is very easy for beginners to get started with, but it is an
old, poorly designed language, lacking in almost every modern
feature. Visual BASIC adds a lot to "good 'ol BASIC", but it is not
appropriate (I believe) to teach a single-platform proprietary
language. And it's still not really a good language....
C
#include
int main(int argc, char*argv[])
{
int a,b,c;
scanf("%d",&a);
scanf("%d",&b);
c = a+b;
printf("%d\n",c);
}
%> gcc -o add add.c
%> ./add
Time to write:
about three minutes, including debugging.
Things to explain:
- #include, functions (main), return types, argc, argv
- variables, types (int)
- scanf (and pretty soon it's limitations and how to work around them)
- printf, format strings
- pointers (already!!)
- compiling, braces and semicolons
Pros and Cons
C was designed by top hackers for their own use. It was designed for
writing operating systems, compilers and other system tools, and in
this role it has become almost totally dominant.
It can provide excellent performance (assuming good choice of
algorithm and good C skills) and allows low level hardware access, but
these are not normally things required by the beginner. C's use of
pointers are a source of frustration and confusion for beginners, but
they are essential in even fairly trivial programs (like the one
above, albeit in a trivial way).
Further, C's string handling is weak compared to many other modern
languages (the scanf function used above is notoriously
problematic).
C is a major and very important language, and all programmers should
have significant exposure to it. It is however a terrible language to
teach beginners. There is too much C that has to be explained,
leaving less time for explaining programming.
Java
import java.io.*;
public class Addup
{
static public void main(String args[]) {
InputStreamReader stdin = new InputStreamReader(System.in);
BufferedReader console = new BufferedReader(stdin);
int i1 = 0,i2 = 0;
String s1,s2;
try {
s1 = console.readLine();
i1 = Integer.parseInt(s1);
s2 = console.readLine();
i2 = Integer.parseInt(s2);
}
catch(IOException ioex) {
System.out.println("Input error");
System.exit(1);
}
catch(NumberFormatException nfex) {
System.out.println("\"" + nfex.getMessage() + "\" is not numeric");
System.exit(1);
}
System.out.println(i1 + " + " + i2 + " = " + (i1+i2));
System.exit(0);
}
}
%> javac Addup.java
%> java Addup
Time to write:
19 minutes! Actually, I spent about 15 minutes,
failed, then searched Google for an example. The code above is copied
from , which, tellingly I thought, starts with the words "It might
be thought that a programme that reads in two user entered integers
and prints out their sum would be a simple piece of code".
Obviously, this code is not perfectly equivalent to the other programs
presented here since it does proper error checking, however Java makes
it difficult not to do error checking. You must catch the
exceptions, and having caught them you might as well do something with
them.
I'm actually kind of embarassed I had so much trouble with this - I've
been working on a commercial Java package for two years, but because
it's GUI based I rarely have to deal with reading from the
console. Real Java programmers will probably look down on me with a
mixture of pity and disgust. Such is life.
Things to explain
- import, classes, semicolons braces
- public, static, void, String, main args[]
- InputStreamReader, BufferedReader, System.in
- variables, types
- try, catch, exceptions, readLine, parseInt
- System.out.println, compiling, running
Pros and Cons
Java is a useful language for cross-platform GUI development, is a
robust platform for OO development, and has an extensive and highly
evolved set of class libraries. Perhaps most importantly, it's the
most popular language around and there's lots of jobs for Java
programmers.
The extensive class library is however quite daunting. It appears
there's a class for almost everything, and much of "programming in
Java" seems to consist of "searching for the right class". Even after
two years I find I cannot do much in Java without constant reference
to the documentation.
Java enforces Object Orientation, exception checking and strict typing
- these are all (arguably) good things - they make it easier for a
group of programmers to robustly create large systems. But for small
problems (such as those faced in introductory programming classes)
these things become nothing more than a complicated, time-sucking
burden.
The employment reason alone is sufficient to make Java a "must teach"
lanaguage, but I believe we do our students a disservice if this is
the best language we show them.
Python
import sys
a = sys.stdin.readline()
b = sys.stdin.readline()
c = int(a) + int(b)
print c
%> python add.py
Time to write:
about one minute, including testing and debugging.
Things to explain
- import
- variables
- sys.stdin
- readline (reads a string)
- int (converts a string to an integer)
- print
Pros and Cons
Python has an awful lot of good points:
- enforces good programming style (indentation is meaningful)
- OO available but not enforced
- Exceptions used but not enforced
- is not a toy or academic language - much real world work is done in Python
- allows concentration on algorithms and problem, not on language features and shortcoming.
- is cross platform and has a powerful set of libraries
- is safe - it has dynamic run time type checking and bounds checking on arrays
- has powerful built-in data types - dictionaries, lists, sequences, functions, sets (in 2.4)
- has powerful built-in control structures - simple looping over
sequences, map, generators, list comprehensions, regular
expressions...
- requires less lines of code for any given problem, and is more
readable - thus greater productivity.
For teaching as a first language however it has some specific
advantages. As can be seen from the examples above (ignoring BASIC),
Python requires less time, less lines of code, and less concepts to be
taught to reach a given goal. This allows more time to be spent on the
important things. Further, some common student errors are completely
byassed in Python:
- end of line is end of line (no forgotten semicolons)
- no type declarations
- true block structure always obvious (no missing braces error)
- dynamic memory allocation and garbage collection
Finally programming in Python is
fun! Fun and frequent success
breed confidence and interest in the student, who is then better
placed to continue learning to program.
But Python is Just a Scripting Language
Python is often dismissed as "just a scripting language" (Perl and
Ruby also suffer from this silly bigotry). This is simply
incorrect. It is not "just a scripting language" - it is a full
featured very high level language that is ideal for many
applications,
including simple scripting duties.
The fact that you can write "quick and dirty" scripts in Python is an
advantage, not a disadvantage, since scripting is actually an
essential part of professional programming. If students don't know
Python (or Perl, or Ruby, or....), they will waste a lot of time
trying to solve script-like problems in Java.
But Python is Slooooooow
Python is an interpreted language, and this does add some
overhead. Dynamic bounds checking, dynamic typing and other clever
Python things slow it down even further. Python can be orders of
magnitude slower than equivalent C code. However
- Many, many applications are not compute bound. To use a high
performance language for them exemplifies the sin of early
optimisation.
- Python interfaces well to C - enormous gains can be made by coding
critical sections in C
- Time saved coding in Python, and the much greater simplicity of the
code written, allows much more time for experimentation in
more efficient algorithms - often much more fruitful than simply running a bad
algorithm very quickly.
Conclusion
C and Java are important languages - for the concepts they embody, for
the employment prospects, and for the classes of problems they
solve. Students must be given a thorough grounding in these
languages. They do not however form a sufficient arsenal for the
professional programmer - a good "scripting language" is a must - nor
are they good languages to teach students new to programming. They
have a lot of overhead and other impediments that take a lot of the
pleasure out, and make both the student's and the teacher's jobs more
difficult than they ought to be.
There are people who would argue that the impediments are part of the
discipline of programming - students must learn to catch their
exceptions, use pointers, declare all their types and so forth. Maybe,
maybe not - but there's time for that later. Let's let students have
the simple joy of small successes that we (well, "I" anyway) had when
we were starting.
Patrick Jordan - patrick@ariel.com.au - 2004-12-14
Postscript (Feb 2006)
Aside from the comments above, a vast number of people wrote to me after
this article appeared on Daily Python to point out that there was a
simpler way to do it in Python:
a = input()
b = input()
c = a + b
print c
%> python add.py
(various one liners like 'print input()+input()' were also suggested
and work just as well but I'd argue are less useful for teaching
purposes). Further, since input() accepts any valid Python expression,
this program just works for a whole range of inputs - ints, floats,
strings (it'll concatenate them - but note that they must be in quotes
else they'll be interpreted as variable names) or expressions such as
"3.14**2". Further proof, as if it was needed, of the beauty of
Python.
