从基础到进阶详解Python字符串拼接的6种方法

str1 = "Hello"
str2 = "World"
result = str1 + " " + str2
print(result)  # 输出: Hello World

# 拼接100个字符串
parts = ["Part" + str(i) for i in range(100)]
result = ""
for part in parts:
    result += part  # 每次循环都创建新字符串

import timeit

def plus_concat():
    s = ""
    for i in range(10000):
        s += str(i)
    return s

print(timeit.timeit(plus_concat, number=100))  # 约2.5秒

words = ["Hello", "World", "Python"]
result = " ".join(words)
print(result)  # 输出: Hello World Python

# 使用join拼接100个字符串
parts = ["Part" + str(i) for i in range(100)]
result = "".join(parts)  # 只需一次内存分配

def join_concat():
    parts = [str(i) for i in range(10000)]
    return "".join(parts)

print(timeit.timeit(join_concat, number=100))  # 约0.05秒

name = "Alice"
age = 25
result = f"My name is {name} and I'm {age} years old."
print(result)  # 输出: My name is Alice and I'm 25 years old.

result = "My name is {} and I'm {} years old.".format(name, age)

def fstring_concat():
    return "".join([f"Part{i}" for i in range(10000)])

def format_concat():
    return "".join(["Part{}".format(i) for i in range(10000)])

print(timeit.timeit(fstring_concat, number=100))  # 约0.1秒
print(timeit.timeit(format_concat, number=100))  # 约0.2秒

name = "Bob"
age = 30
result = "My name is %s and I'm %d years old." % (name, age)
print(result)

def percent_concat():
    return "".join(["Part%d" % i for i in range(10000)])

print(timeit.timeit(percent_concat, number=100))  # 约0.25秒

from string import Template

t = Template("My name is $name and I'm $age years old.")
result = t.substitute(name="Charlie", age=35)
print(result)

# 用户提供的模板
user_template = "Hello, ${username}! Your balance is $${balance:.2f}"
t = Template(user_template)
result = t.substitute(username="dave", balance=1234.567)
print(result)  # 输出: Hello, dave! Your balance is $1234.57

def template_concat():
    t = Template("Part$i")
    return "".join([t.substitute(i=i) for i in range(10000)])

print(timeit.timeit(template_concat, number=100))  # 约1.2秒

# 拼接多个字节串
byte_parts = [b"Hello", b" ", b"World"]
result = b"".join(byte_parts)
print(result)  # 输出: b'Hello World'

# 使用bytearray动态构建
ba = bytearray()
ba.extend(b"Hello")
ba.extend(b" ")
ba.extend(b"World")
print(ba)  # 输出: bytearray(b'Hello World')

def bytearray_concat():
    ba = bytearray()
    for i in range(10000):
        ba.extend(str(i).encode())
    return ba

print(timeit.timeit(bytearray_concat, number=100))  # 约0.3秒

import timeit
from string import Template

def test_methods():
    # 准备测试数据
    parts = [str(i) for i in range(1000)]
    
    # 定义测试函数
    def plus():
        s = ""
        for part in parts:
            s += part
        return s
    
    def join():
        return "".join(parts)
    
    def fstring():
        return "".join([f"{part}" for part in parts])
    
    def format_method():
        return "".join(["{}".format(part) for part in parts])
    
    def percent():
        return "".join(["%s" % part for part in parts])
    
    def template():
        t = Template("$part")
        return "".join([t.substitute(part=part) for part in parts])
    
    # 运行测试
    methods = {
        "加号": plus,
        "join": join,
        "f-string": fstring,
        "format": format_method,
        "%格式化": percent,
        "Template": template
    }
    
    for name, func in methods.items():
        time = timeit.timeit(func, number=1000)
        print(f"{name:<10}: {time:.4f}秒")

test_methods()

# 正确做法
names = ["Alice", "Bob", "Charlie"]
greeting = ", ".join(names) + "!"

# 避免的做法
greeting = ""
for name in names:
    greeting += name + ", "
greeting = greeting[:-2] + "!"  # 需要处理多余逗号

# 正确做法
user = {"name": "Alice", "age": 25}
message = f"{user['name']} is {user['age']} years old."

# 避免的做法
message = "".join([user['name'], " is ", str(user['age']), " years old."])

# 正确做法
from string import Template
user_template = input("Enter template: ")
t = Template(user_template)
try:
    result = t.substitute(name="Alice", age=25)
except KeyError as e:
    print(f"Missing variable: {e}")

# 避免的做法 - 存在代码注入风险
# user_template = input("Enter template: ")  # 用户可能输入恶意代码
# result = user_template.format(name="Alice", age=25)

# 正确做法
def build_packet(data_parts):
    ba = bytearray()
    for part in data_parts:
        ba.extend(part.encode())
    return ba

# 避免的做法
def bad_build_packet(data_parts):
    s = ""
    for part in data_parts:
        s += part
    return s.encode()  # 需要两次内存分配

class StringJoiner:
    def __init__(self, separator=""):
        self.separator = separator
        self.parts = []
    
    def add(self, part):
        self.parts.append(str(part))
        return self  # 支持链式调用
    
    def __str__(self):
        return self.separator.join(self.parts)

# 使用示例
joiner = StringJoiner(", ")
joiner.add("Apple").add("Banana").add("Cherry")
print(joiner)  # 输出: Apple, Banana, Cherry