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Python内置函数的用法实例教程

Jun 16, 2016 am 08:42 AM
python built-in functions usage

本文简单的分析了Python中常用的内置函数的用法,分享给大家供大家参考之用。具体分析如下:

一般来说,在Python中内置了很多有用的函数,我们可以直接调用。

而要调用一个函数,就需要知道函数的名称和参数,比如求绝对值的函数abs,只有一个参数。可以直接从Python的官方网站查看文档:http://docs.python.org/2/library/functions.html#abs

也可以在交互式命令行通过help(abs)查看abs函数的帮助信息。

调用abs函数:

>>> abs(100)
100
>>> abs(-20)
20
>>> abs(12.34)
12.34

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调用函数的时候,如果传入的参数数量不对,会报TypeError的错误,并且Python会明确地告诉你:abs()有且仅有1个参数,但给出了两个:

>>> abs(1, 2)
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: abs() takes exactly one argument (2 given)

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如果传入的参数数量是对的,但参数类型不能被函数所接受,也会报TypeError的错误,并且给出错误信息:str是错误的参数类型:

>>> abs('a')
Traceback (most recent call last):
 File "<stdin>", line 1, in <module>
TypeError: bad operand type for abs(): 'str'

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而比较函数cmp(x, y)就需要两个参数,如果xy,返回1:

>>> cmp(1, 2)
-1
>>> cmp(2, 1)
1
>>> cmp(3, 3)
0

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数据类型转换

Python内置的常用函数还包括数据类型转换函数,比如int()函数可以把其他数据类型转换为整数:

>>> int('123')
123
>>> int(12.34)
12
>>> float('12.34')
12.34
>>> str(1.23)
'1.23'
>>> unicode(100)
u'100'
>>> bool(1)
True
>>> bool('')
False

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函数名其实就是指向一个函数对象的引用,完全可以把函数名赋给一个变量,相当于给这个函数起了一个“别名”:

>>> a = abs # 变量a指向abs函数
>>> a(-1) # 所以也可以通过a调用abs函数
1

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小结:

调用Python的函数,需要根据函数定义,传入正确的参数。如果函数调用出错,一定要学会看错误信息,所以英文很重要!

希望本文所述实例对大家Python程序设计有所帮助。

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