一、多行编写“长字符串”

1.1 直接三引号””” “””

multi_line_string = """this is line number 1
this is line number 2
this is line number 3
this is line number 4"""
 
print(multi_line_string)
 
# this is line number 1
# this is line number 2
# this is line number 3
# this is line number 4

这种多行字符串的劣势在于：输入的时候换行，那么这个字符串在换行的位置插入了一个\n符号，所以严格来说并不能实现我们所说的

输出一行长字符串但是输入的形式是多行

。

注意，单双引号，输入形式不允许是多行但不加反斜杠符号。代码如下所示，出错了。

multi_line_string = "this is line number 1
this is line number 2
this is line number 3
this is line number 4"
 
print(multi_line_string)
 
# SyntaxError: EOL while scanning string literal

如果不想换行，可以在行尾添加反斜杠。

multi_line_string = """this is line number 1\
this is line number 2\
this is line number 3\
this is line number 4"""
 
print(multi_line_string)
 
# this is line number 1this is line number 2this is line number 3this is line number 4

1.2 单双引号和反斜杠

multi_line_string = "this is line number 1\
this is line number 2\
this is line number 3\
this is line number 4"
 
print(multi_line_string)
 
# this is line number 1this is line number 2this is line number 3this is line number 4

1.3 单双引号和圆括号

每一行字符串，都需要加一对单双引号；最后输出的是一行字符串。

multi_line_string = ("this is line number 1"
"this is line number 2"
"this is line number 3"
"this is line number 4")
 
print(multi_line_string)
 
# this is line number 1this is line number 2this is line number 3this is line number 4

将圆括号和反斜杠符配合，在每一次换行的位置加反斜杠，就可以在这多行字符串上只加一对单双引号了。

multi_line_string = ("this is line number 1\
this is line number 2\
this is line number 3\
this is line number 4")
 
print(multi_line_string)
 
# this is line number 1this is line number 2this is line number 3this is line number 4

1.4 易错点：禁止存在缩进

在编程的时候，如果处于if、for语句的代码块内，字符串在手动换行时可能会自动缩进；这时候编译器没办法把这些缩进去除，从而影响输出结果。

multi_line_string = """this is line number 1\
                       this is line number 2\
                       this is line number 3\
                       this is line number 4"""
 
print(multi_line_string)
 
# this is line number 1                       this is line number 2                       this is line number 3                       this is line number 4

二、多行编写“长推导式”

要想多行形式写入长推导式，可以直接换行，比如下面的代码

class_list = [c for c in os.listdir(all_file_dir) 
              if os.path.isdir(os.path.join(all_file_dir, c)) 
              and not c.endswith('Set') 
              and not c.startswith('.')]

同时，为了增强可读性 ，建议一块一块地换行，比如and逻辑语句的前一块和后一块。

三、多行编写“长序列”

只要你每一次换行不拆分一个单独的数，就不会出问题。

list1 = [1,
         2,
         3,
         4]

print(list1)

# [1, 2, 3, 4]

由于换行不作为数与数之间的分隔符，所以下面的第二个代码块就出错了。

list1 = [1,
         22,
         3,
         4]

print(list1) # [1, 22, 3, 4]



# ---------------------------------

list1 = [1,
         2
         2,
         3,
         4]

print(list1)  # SyntaxError: invalid syntax