[英]Python - can you “refresh” a variable to re-initialize with new sub-variables?
假設我想聲明一個字符串供整個班級使用,但該字符串有一部分可能會在以后更改。 是否可以只聲明一次字符串,然后“刷新”它?
例子:
substring = ""
my_long_string = f"This is a long string using another {substring} in it."
def printMyString(newString):
substring = newString
print(my_long_string)
printMyString(newString="newer, better substring")
我可以調整此代碼,以便最終打印出This is a long string using another newer, better substring in it.
但在后來再次宣布長字符串?
我唯一的猜測是這樣的:
substring = ""
def regenerate_string(substring):
return f"This is a long string using another {substring} in it."
def printMyString(newString):
print(regenerate_string(newString))
printMyString(newString="newer, better substring")
但我想問一下 Python 中是否可能有一個內置函數來做到這一點?
不要使用f-string
,使用占位符{}
聲明模板字符串並在必要時使用format()
my_long_string = "This is a long string using another {} in it."
print(my_long_string.format("newer, better substring")) # This is a long string using another newer, better substring in it.
print(my_long_string.format("some other substring")) # This is a long string using another some other substring in it.
您可以通過這種方式插入任意數量的子字符串
string = "With substrings, this {} and this {}."
print(string.format("first", "second")) # With substrings, this first and this second.
您還可以使用變量
string = "With substrings, this {foo} and this {bar}."
print(string.format(foo="first", bar="second")) # With substrings, this first and this second.
print(string.format(bar="first", foo="second")) # With substrings, this second and this first.
這不起作用的原因是因為您將my_long_string
聲明為函數f"This is a long string using another {substring} in it."
的返回值f"This is a long string using another {substring} in it."
,而不是函數本身。
如果您想在示例中使用您打算使用的子字符串,則需要將my_long_string
聲明為lambda : f"This is a long string using another {substring} in it."
,這會在substring
更改時更改返回值。
但就像蓋伊說的, my_long_string.format(substring)
是完全合理的。
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