In modern programming, strings are an indispensable data type.
Whether it is handling user input, file reading and writing, or network communication, strings play a core role.
However, string processing does not simply splice characters together, it involves character sets, encoding, and the underlying implementation of programming languages.
This article will explore in-depth how strings are processed in programs, especially inPythondevelopment in
At the same time, compare the string implementation methods of other programming languages and comparePythonLooking forward to the future development direction of strings.
1. How the program handles strings
1.1. Character Sets and Encoding
In a computer, a string is a sequence of characters, and characters are essentially represented by encoding.
Character Set（Character Set) defines a collection of characters, commonly used asASCII、UnicodeAndcoding（Encoding) is the rule for mapping characters in the character set to a sequence of bytes.
Different encoding methods determine the character in the computerstorageandtransmissionWay.
1.2. Widely used UTF-8
UTF-8It is one of the most widely used character encodings at present, and it can be expressed efficientlyUnicodeCharacter set.
UTF-8The advantage is that it is compatibleASCII,forASCIIcharacter,UTF-8Encoded using only one byte, and 2 to 4 bytes for other characters.
This design makesUTF-8Excellent in storage and transfer efficiency, especially when dealing with multilingual text.
# Define a string containing Chinese characters
s = "Hello"
# Encoding with UTF-8
utf8_encoded = ("utf-8")
print(utf8_encoded) # Output: b'\xe4\xbd\xa0\xe5\xa5\xbd'
# Encoding with GBK
gbk_encoded = ("gbk")
print(gbk_encoded) # Output: b'\xc4\xe3\xba\xc3'In this example, the same string"Hello",useUTF-8The byte sequence obtained after encoding and useGBKThe sequence of bytes obtained after encoding is different.
When we need to convert the byte sequence back to a string, we must use the corresponding encoding method to decode it, otherwise garbled code will occur.
2. The development of Python strings
existPythonEarlier versions (Python 2There is some confusion in string processing.
Python 2There are two string types:strandunicode。
strIt is actually a byte string, which can represent any sequence of bytes, andunicodeIt's the real oneUnicodeString.
This design leads to prone to encoding errors and confusion when dealing with multilingual text.Python2Everyone knows the trouble of dealing with Chinese strings.
arrivePython 3, major improvements to string types.
Python 3In-housestrThe type is realUnicodestring, andbytesType is used to represent a sequence of bytes.
This design makes string processing clearer and more consistent.
3. Implementation in CPython
CPythonThe string implementation in the string is carefully designed to balance memory footprint and performance.
Through dynamic encoding selection, caching mechanism and compact storage,CPythonAbility to process multilingual text efficiently.
At the same time, rich string methods and efficient encoding and decoding mechanisms make string operations both simple and efficient.
This design makes Python a powerful tool for processing text data.
3.1. Internal representation
existCPythonIn, the string isUnicodeCharacter sequences are stored dynamically using multiple encoding methods internally to balance memory footprint and performance.
Its mainInternal structureinclude:
-
PyASCIIObject: Used to store only containsASCIIA string of characters. This string can be directlyUTF-8Format storage, high access efficiency -
PyCompactUnicodeObject: Used to store strings containing **non-ASCII characters. It supports multiple encoding methods, such asUCS-1(Single byte),UCS-2(double bytes) andUCS-4(Four bytes), which encoding is used depends on the maximum Unicode code point of the character in the string. -
PyUnicodeObject: Used to be compatible with older versions of the API, and supports dynamic conversion to other representations.
3.2. Dynamic encoding selection
CPythonAutomatically select the most appropriate encoding method according to the content of the string:
If the string contains only ASCII characters (code point range U+0000 to U+007F), use UCS-1 encoding (single byte);
If the string contains non-ASCII characters, but the code points range between U+0080 and U+FFFF, UCS-2 encoding (double bytes);
If the string contains characters that exceed U+FFFFF (such as some emojis), UCS-4 encoding (four bytes).
This dynamic selection mechanism makesPythonStrings are both efficient and flexible when dealing with multilingual text.
3.3. Immutability of strings
existPythonIn, a string is an immutable object, and once created, the content of the string cannot be modified.
This design allows strings to be safely shared and cached.
For example, the hash value of a string is calculated once at creation time and can be used directly later without recalculating.
typedef struct {
PyObject_HEAD
Py_ssize_t length; // string length
Py_hash_t hash; // The hash value of the string
struct {
unsigned int interned:2; // Whether it is cached
unsigned int kind:2; // encoding type (UCS-1/UCS-2/UCS-4)
unsigned int compact:1; // Is it compact storage
unsigned int ascii:1; // Is it an ASCII string
unsigned int ready:1; // Whether it has been initialized
} state;
wchar_t *wstr; // Used to store wide character representations
} PyASCIIObject;3.4. Encoding and decoding
CPythonIt provides an efficient encoding and decoding mechanism, and supports multiple character sets (such as UTF-8, UTF-16, GBK, etc.).
Encoding and decoding of strings is passedencode()anddecode()Method implementation:
# Encoding: Convert Unicode strings to byte sequences
text = "Hello, Python"
bytes_data = ("utf-8")
print(bytes_data) # b'\xe4\xbd\xa0\xe5\xa5\xbd\xef\xbc\x8cPython'
# Decoding: Convert byte sequences back to Unicode strings
decoded_text = bytes_data.decode("utf-8")
print(decoded_text) # Hello, PythonInside,CPythonuseUTF-8As the default encoding, because it is compatibleASCIIAnd suitable for multilingual support.
3.5. Performance optimization
CPythonMultiple optimizations are made in string processing:
-
Cache mechanism: For common string operations (such as
intern()），CPythonWill cache the results to avoid repeated calculations -
Compact storage: Dynamically select the encoding method,
CPythonCan reduce memory usage while ensuring performance -
Delay decoding: For strings that need to be used multiple times,
CPythonDecode the decoding operation until it is really needed
4. Comparison with strings in other languages
Comparing strings with mainstream programming languages can give us a better understanding ofPythonThe pros and cons of strings.
The following programming languages have their own characteristics in string implementation:
- C language focuses on underlying control
- Go and Rust focus on security and UTF-8 support
- Java focuses on ease of use and security
The design of each language reflects its goals and application scenarios.
4.1. Character strings in C language
existCIn languages, strings are usually represented by character arrays, and are empty characters.'\0'As the end flag of the string.
CThe standard library provides a series of functions to process strings, such asstrcpy、strcmpwait.
However,CThe language's string processing is not directly supportedUnicode,For multilingual text processing, additional libraries are required or manual processing of encoding conversion is required.
To support multibyte character sets,CIntroducedwchar_ttype, but its size is platform-dependent, which complicates cross-platform development.
4.2. Character strings in Go
GoThe language's string is a read-only byte slice, andGoThe language source files are used by defaultUTF - 8coding.
GoLanguage string support is supported throughforLoop iterates over bytes or useruneType iterationUnicodeCode point.
The standard library provides a wealth of functions to handle strings, including string search, replacement, and encoding conversion.
4.3. Strings in Java
JavaThe string in the language isStringAn instance of a class, it is immutable.
JavaString internal useUTF-16Encoding to store characters, each character takes up 2 bytes for characters in the basic multitext plane (BMP).
JavaProvides rich string operation methods andStringClass andStringBuilderclass, developers can efficiently process strings.
JavaThe string design focuses on security, but its internalUTF-16Coding is being processedASCIISpace may be wasted when texting.
4.4. Strings in Rust
RustThe main string type of the language isstr, it is aUTF - 8Encoded immutable string slices.
RustIt does not support direct access to characters in a string through integer indexes, but providesbytesandcharsMethod to iterate through bytes and code points respectively.
RustString processing emphasizes security and efficiency, and avoids common string operation errors through ownership and borrowing mechanisms.
5. Summary
Anyway,PythonThe design goal of strings is toflexibilityandefficiencystrike a balance.
BystrType design isUnicodestring,PythonIt can easily handle multilingual text, meeting the needs of modern applications for globalization.
at the same time,CPythonSome optimization strategies are adopted in string implementation, such as string residency (string interning) and other technologies have improved the efficiency of string operation.
With the programming communityUTF-8Widely recognized and used in coding,PythonWill similar use be adopted in the futureGoorRustofUTF-8The dominant string implementation is a question worth discussing.
at presentPythonThe string implementation has been able to support multilingual text processing well and has achieved a good balance in efficiency and flexibility.
However, if the futurePythonThe community believes that further optimizationUTF-8Processing performance or simplifying the string processing model is necessary, so refer to itGoorRustThe implementation method may be one direction.