Python join() 字串合併
join() 方法用來將序列中的元素用指定的字串連接起來。
基本用法
words = ["Hello", "World", "Python"]
result = " ".join(words)
print(result) # Hello World Python
語法
str.join(iterable)
str：用來連接元素的字串iterable：要連接的可迭代物件（元素必須是字串）
不同的連接符號
words = ["apple", "banana", "orange"]
# 空格連接
print(" ".join(words)) # apple banana orange
# 逗號連接
print(",".join(words)) # apple,banana,orange
# 逗號加空格
print(", ".join(words)) # apple, banana, orange
# 換行連接
print("\n".join(words))
# apple
# banana
# orange
# 無間隔連接
print("".join(words)) # applebananaorange
# 自訂分隔符號
print(" | ".join(words)) # apple | banana | orange
連接不同類型的序列
# List
my_list = ["a", "b", "c"]
print("-".join(my_list)) # a-b-c
# Tuple
my_tuple = ("x", "y", "z")
print("-".join(my_tuple)) # x-y-z
# Set（順序不固定）
my_set = {"1", "2", "3"}
print("-".join(my_set)) # 順序可能不同
# 字串（每個字元）
text = "Hello"
print("-".join(text)) # H-e-l-l-o
連接數字
join() 只能連接字串，數字需要先轉換：
numbers = [1, 2, 3, 4, 5]
# 錯誤：數字不能直接 join
# result = ",".join(numbers) # TypeError
# 正確：先轉換為字串
result = ",".join(str(n) for n in numbers)
print(result) # 1,2,3,4,5
# 或使用 map
result = ",".join(map(str, numbers))
print(result) # 1,2,3,4,5
實際範例
建立 CSV 行
data = ["Alice", "25", "Taipei", "Engineer"]
csv_line = ",".join(data)
print(csv_line) # Alice,25,Taipei,Engineer
建立 URL 路徑
parts = ["users", "123", "profile"]
path = "/".join(parts)
print(f"/{path}") # /users/123/profile
建立 SQL 查詢
columns = ["name", "age", "city"]
values = ["'Alice'", "25", "'Taipei'"]
sql = f"INSERT INTO users ({', '.join(columns)}) VALUES ({', '.join(values)})"
print(sql)
# INSERT INTO users (name, age, city) VALUES ('Alice', 25, 'Taipei')
建立 HTML 列表
items = ["Python", "JavaScript", "Go"]
html = "<ul>\n" + "\n".join(f" <li>{item}</li>" for item in items) + "\n</ul>"
print(html)
輸出：
<ul>
<li>Python</li>
<li>JavaScript</li>
<li>Go</li>
</ul>
過濾空字串後連接
parts = ["hello", "", "world", "", "python"]
# 過濾空字串
result = " ".join(filter(None, parts))
print(result) # hello world python
# 或用 list comprehension
result = " ".join(p for p in parts if p)
print(result) # hello world python
格式化輸出
# 將數字格式化為電話號碼
digits = "0912345678"
formatted = "-".join([digits[:4], digits[4:7], digits[7:]])
print(formatted) # 0912-345-678
搭配 split() 使用
# 移除多餘空白
text = " hello world python "
result = " ".join(text.split())
print(result) # hello world python
# 替換分隔符號
csv = "a,b,c,d"
tsv = "\t".join(csv.split(","))
print(tsv) # a b c d
# 反轉單字順序
sentence = "Hello World Python"
reversed_sentence = " ".join(sentence.split()[::-1])
print(reversed_sentence) # Python World Hello
效能考量
join() 比字串相加 + 更有效率：
# 不好的做法（效率較低）
result = ""
for word in ["a", "b", "c", "d", "e"]:
result += word + ","
# 好的做法（效率較高）
result = ",".join(["a", "b", "c", "d", "e"])
當連接大量字串時，join() 的效能差異會更明顯。