string 拼接

可以使用 + 实现两个字符串的拼接。

a = "Hello"
b = "World"
c = a + b
print(c)

--- output ---

PS E:\dream\markdown\python> & "C:/Program Files (x86)/Python/python.exe" e:/dream/markdown/python/app/app.py
HelloWorld

如果想调整一下格式，可以在 hellworld 之间加上空格，如下所示：

a = "Hello"
b = "World"
c = a + " " + b
print(c)

--- output ---

PS E:\dream\markdown\python> & "C:/Program Files (x86)/Python/python.exe" e:/dream/markdown/python/app/app.py
Hello World

string 格式化

还记得在前面的文章中提到，将 string 和 int 进行拼接是行不通的，这时候的解决方案就是用 format ,先看一下之前的例子。

age = 36
txt = "My name is John, I am " + age
print(txt)

--- output ---

PS E:\dream\markdown\python> & "C:/Program Files (x86)/Python/python.exe" e:/dream/markdown/python/app/app.py
Traceback (most recent call last):
  File "e:/dream/markdown/python/app/app.py", line 2, in 
    txt = "My name is John, I am " + age
TypeError: can only concatenate str (not "int") to str

接下来看看 format，在字符串中设置一个占位符 {}，占位符的参数通过 format 传入，如下所示：

age = 36
txt = "My name is John, and I am {}"
print(txt.format(age))

PS E:\dream\markdown\python> & "C:/Program Files (x86)/Python/python.exe" e:/dream/markdown/python/app/app.py
My name is John, and I am 36

有些朋友可能就要问了，既然支持一个 占位符，那能不能支持多个占位符呢？ 当然可以啦，如下所示：

quantity = 3
itemno = 567
price = 49.95
myorder = "I want {} pieces of item {} for {} dollars."
print(myorder.format(quantity, itemno, price))

--- output ---

PS E:\dream\markdown\python> & "C:/Program Files (x86)/Python/python.exe" e:/dream/markdown/python/app/app.py
I want 3 pieces of item 567 for 49.95 dollars.

除了这种通用的占位符，还可以使用类似 C# 中的数字型占位符形式，实现精准指向性占位。

quantity = 3
itemno = 567
price = 49.95
myorder = "I want to pay {2} dollars for {0} pieces of item {1}."
print(myorder.format(quantity, itemno, price))

--- output ---

PS E:\dream\markdown\python> & "C:/Program Files (x86)/Python/python.exe" e:/dream/markdown/python/app/app.py
I want to pay 49.95 dollars for 3 pieces of item 567.

更多高质量干货：参见我的 GitHub: github.com/ctripxchuang/python