130 lines
6.6 KiB
Plaintext
130 lines
6.6 KiB
Plaintext
Comparing Python to Other Languages
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-----------------------------------
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These comparisons are a personal view. Comments are requested.
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--Guido van Rossum <guido@python.org>
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Python is often compared to other interpreted languages such as Java,
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JavaScript, Perl, Tcl, or Smalltalk. Comparisons to C++, Common Lisp
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and Scheme can also be enlightening. In this section I will briefly
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compare Python to each of these languages. These comparisons
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concentrate on language issues only. In practice, the choice of a
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programming language is often dictated by other real-world constraints
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such as cost, availability, training, and prior investment, or even
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emotional attachment. Since these aspects are highly variable, it
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seems a waste of time to consider them much for this publication.
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Java
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Python programs are generally expected to run slower than Java
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programs, but they also take much less time to develop. Python
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programs are typically 3-5 times shorter than equivalent Java
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programs. This difference can be attributed to Python's built-in
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high-level data types and its dynamic typing. For example, a Python
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programmer wastes no time declaring the types of arguments or
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variables, and Python's powerful polymorphic list and dictionary
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types, for which rich syntactic support is built straight into the
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language, find a use in almost every Python program. Because of the
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run-time typing, Python's run time must work harder than Java's. For
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example, when evaluating the expression a+b, it must first inspect the
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objects a and b to find out their type, which is not known at compile
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time. It then invokes the appropriate addition operation, which may be
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an overloaded user-defined method. Java, on the other hand, can
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perform an efficient integer or floating point addition, but requires
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variable declarations for a and b, and does not allow overloading of
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the + operator for instances of user-defined classes.
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For these reasons, Python is much better suited as a "glue" language,
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while Java is better characterized as a low-level implementation
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language. In fact, the two together make an excellent
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combination. Components can be developed in Java and combined to form
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applications in Python; Python can also be used to prototype
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components until their design can be "hardened" in a Java
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implementation. To support this type of development, a Python
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implementation written in Java is under development, which allows
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calling Python code from Java and vice versa. In this implementation,
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Python source code is translated to Java bytecode (with help from a
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run-time library to support Python's dynamic semantics).
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Javascript
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Python's "object-based" subset is roughly equivalent to
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JavaScript. Like JavaScript (and unlike Java), Python supports a
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programming style that uses simple functions and variables without
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engaging in class definitions. However, for JavaScript, that's all
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there is. Python, on the other hand, supports writing much larger
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programs and better code reuse through a true object-oriented
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programming style, where classes and inheritance play an important
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role.
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Perl
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Python and Perl come from a similar background (Unix scripting, which
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both have long outgrown), and sport many similar features, but have a
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different philosophy. Perl emphasizes support for common
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application-oriented tasks, e.g. by having built-in regular
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expressions, file scanning and report generating features. Python
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emphasizes support for common programming methodologies such as data
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structure design and object-oriented programming, and encourages
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programmers to write readable (and thus maintainable) code by
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providing an elegant but not overly cryptic notation. As a
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consequence, Python comes close to Perl but rarely beats it in its
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original application domain; however Python has an applicability well
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beyond Perl's niche.
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Tcl
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Like Python, Tcl is usable as an application extension language, as
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well as a stand-alone programming language. However, Tcl, which
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traditionally stores all data as strings, is weak on data structures,
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and executes typical code much slower than Python. Tcl also lacks
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features needed for writing large programs, such as modular
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namespaces. Thus, while a "typical" large application using Tcl
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usually contains Tcl extensions written in C or C++ that are specific
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to that application, an equivalent Python application can often be
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written in "pure Python". Of course, pure Python development is much
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quicker than having to write and debug a C or C++ component. It has
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been said that Tcl's one redeeming quality is the Tk toolkit. Python
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has adopted an interface to Tk as its standard GUI component library.
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Smalltalk
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Perhaps the biggest difference between Python and Smalltalk is
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Python's more "mainstream" syntax, which gives it a leg up on
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programmer training. Like Smalltalk, Python has dynamic typing and
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binding, and everything in Python is an object. However, Python
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distinguishes built-in object types from user-defined classes, and
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currently doesn't allow inheritance from built-in types. Smalltalk's
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standard library of collection data types is more refined, while
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Python's library has more facilities for dealing with Internet and WWW
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realities such as email, HTML and FTP. Python has a different
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philosophy regarding the development environment and distribution of
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code. Where Smalltalk traditionally has a monolithic "system image"
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which comprises both the environment and the user's program, Python
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stores both standard modules and user modules in individual files
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which can easily be rearranged or distributed outside the system. One
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consequence is that there is more than one option for attaching a
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Graphical User Interface (GUI) to a Python program, since the GUI is
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not built into the system.
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C++
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Almost everything said for Java also applies for C++, just more so:
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where Python code is typically 3-5 times shorter than equivalent Java
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code, it is often 5-10 times shorter than equivalent C++ code!
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Anecdotal evidence suggests that one Python programmer can finish in
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two months what two C++ programmers can't complete in a year. Python
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shines as a glue language, used to combine components written in C++.
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Common Lisp and Scheme
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These languages are close to Python in their dynamic semantics, but so
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different in their approach to syntax that a comparison becomes almost
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a religious argument: is Lisp's lack of syntax an advantage or a
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disadvantage? It should be noted that Python has introspective
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capabilities similar to those of Lisp, and Python programs can
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construct and execute program fragments on the fly. Usually,
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real-world properties are decisive: Common Lisp is big (in every
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sense), and the Scheme world is fragmented between many incompatible
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versions, where Python has a single, free, compact implementation.
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