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变量和类型
Python是完全面向对象的，并且不是“静态类型”的。您不需要在使用变量之前声明它们，或者声明它们的类型。在Python中，每个变量都是一个对象。
本教程将介绍几种基本类型的变量。
Numbers
Python支持两种类型的数字——整数（整数）和浮点数（小数）。（它还支持复数，但本教程不作解释）。
要定义一个整数，请使用以下语法：
myint = 7
print(myint)
要定义一个浮点数，您可以使用以下其中一种表示法：
myfloat = 7.0
print(myfloat)
myfloat = float(7)
print(myfloat)
Strings
字符串可以用单引号或双引号定义。
mystring = 'hello'
print(mystring)
mystring = "hello"
print(mystring)
两者之间的区别是使用双引号可以更容易地包含撇号（否则使用单引号时会终止字符串）。
mystring = "Don't worry about apostrophes"
print(mystring)
还有额外的定义字符串的变体，使其更容易包含诸如回车、反斜杠和Unicode字符之类的内容。这些不在本教程的讨论范围内，但可以在Python文档中找到。
可以对数字和字符串执行简单的操作：
one = 1
two = 2
three = one + two
print(three)
hello = "hello"
world = "world"
helloworld = hello + " " + world
print(helloworld)
可以在同一行“同时”对多个变量进行赋值，如下所示：
a, b = 3, 4
print(a, b)
不支持在数字和字符串之间混合使用操作符：
# This will not work!
one = 1
two = 2
hello = "hello"
print(one + two + hello)
练习
这次练习的目标是创建一个字符串、一个整数和一个浮点数。字符串应该命名为mystring，包含单词"hello"。浮点数应该命名为myfloat，并包含数字10.0，整数应该命名为myint，并包含数字20。
# change this code
mystring = None
myfloat = None
myint = None
# testing code
if mystring == "hello":
print("String: %s" % mystring)
if isinstance(myfloat, float) and myfloat == 10.0:
print("Float: %f" % myfloat)
if isinstance(myint, int) and myint == 20:
print("Integer: %d" % myint)
# change this code
mystring = "hello"
myfloat = 10.0
myint = 20
# testing code
if mystring == "hello":
print("String: %s" % mystring)
if isinstance(myfloat, float) and myfloat == 10.0:
print("Float: %f" % myfloat)
if isinstance(myint, int) and myint == 20:
print("Integer: %d" % myint)
test_object('mystring', incorrect_msg="Don't forget to change `mystring` to the correct value from the exercise description.")
test_object('myfloat', incorrect_msg="Don't forget to change `myfloat` to the correct value from the exercise description.")
test_object('myint', incorrect_msg="Don't forget to change `myint` to the correct value from the exercise description.")
test_output_contains("String: hello",no_output_msg= "Make sure your string matches exactly to the exercise desciption.")
test_output_contains("Float: 10.000000",no_output_msg= "Make sure your float matches exactly to the exercise desciption.")
test_output_contains("Integer: 20",no_output_msg= "Make sure your integer matches exactly to the exercise desciption.")
success_msg("Great job!")
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