為什么我的一根弦在我嘗試后一遍又一遍地重復

Question

我正在嘗試將各種字符串連接在一起以形成一條消息。

理想的 output 如下所示：

The following stocks have changed with more than 0.9%:\
MSFT: 0.05\
TSLA: 0.012\
AAPL: 0.019

下面是我的代碼：

stocks = {
    "MSFT":0.05,
    "TSLA":0.012,
    "AAPL":0.019,
}

subject = 'Opening Price Warnings'
body = 'The following stocks have changed with more than 0.9%: \n'.join([f'{key}: {value}' for key, value in stocks.items()])
msg = f'Subject: {subject}\n\n{body}'
print(msg)

我的代碼一遍又一遍地重復第一行。
我收到這樣的消息：\

MSFT: 0.05The following stocks have changed with more than 0.9%:\
TSLA: 0.012The following stocks have changed with more than 0.9%:\
AAPL: 0.019The following stocks have changed with more than 0.9%:

為什么會這樣？

Answer 1

因為在body中，您將相同的初始字符串連接到 for 循環字符串的所有條目。

have just body = 'The following stocks have changed with more than 0.9%:並創建一個僅包含 dict 元素的新字符串。

stocks = {'MSFT': 0.05, 'TSLA': 0.012}
body1 = 'The following stocks have changed with more than 0.9%: \n'
body2 = '\n'.join([f'{key}: {value}' for key, value in stocks.items()])
body1 + body2
# 'The following stocks have changed with more than 0.9%: \nMSFT: 0.05\nTSLA: 0.012\nAAPL: 0.019'

Answer 2

str.join()不是連接兩個字符串的 function 。

join function 用於插入分隔符。
分隔符分隔字符串容器中的元素。

一個例子如下所示：

eldest_cookie_jar = [
    "red",
    "blue",
    "green"
]

s = "-".join(eldest_cookie_jar)
print(s)

控制台 output 是：

red-blue-green

在上面的示例中，我使用連字符 ( - ) 作為分隔符。
所有 colors 都用連字符分隔。

模式是：

output = delimiter.join(non_delimiters)

非分隔符是字符串形式的實際數據。

如果您想用逗號分隔數字，則將數字轉換為字符串，然后調用str.join() ，如下所示：

stryng = ",".join(numbers)     

如果您想制作三明治，那么我們有：

buns = ["(top bun)", "(bottom bun)"]
meat = "(meat)"

result = meat.join(buns)
print(result)
# "(top bun)(meat)(bottom bun)"

下面還有更多示例； 為了荒謬地詳盡而包括：

eldest_cookie_jar = [
    "red",
    "blue",
    "green"
]

# It is important to convert data to strings
# before using `str.join()` to delimit the data
#
# `map(str, data)` will convert each element
# of `data` into a string.
#

youngest_cookie_jar = tuple(map(str, [0.1, 0.2, 0.3]))

meta_container = [
    eldest_cookie_jar,
    youngest_cookie_jar
]

delims = [
    ", ",
    "...",
    ":--:",
    " ",
    "   ¯\_(ツ)_/¯   "
]

for container in meta_container:
    for delimiter in delims:
        result = delimiter.join(container)
        beginning = "\n----------\n"
        print(result, end=beginning)

控制台 output 是：

red, blue, green
----------
red...blue...green
----------
red:--:blue:--:green
----------
red blue green
----------
red   ¯\_(ツ)_/¯   blue   ¯\_(ツ)_/¯   green
----------
0.1, 0.2, 0.3
----------
0.1...0.2...0.3
----------
0.1:--:0.2:--:0.3
----------
0.1 0.2 0.3
----------
0.1   ¯\_(ツ)_/¯   0.2   ¯\_(ツ)_/¯   0.3
----------