Python3基础 str format 位置参数与关键字参数

 

•        Python : 3.7.0
•          OS : Ubuntu 18.04.1 LTS
•         IDE : PyCharm 2018.2.4
•       Conda : 4.5.11
•    typesetting : Markdown

 

code

coder@Ubuntu:~$ source activate py37
(py37) coder@Ubuntu:~$ ipython
Python 3.7.0 (default, Jun 28 2018, 13:15:42)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.5.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: # 位置参数

In [2]: "{0}{1}{2}{1}{0}".format("a","b","c")  # "a"填的是{0}   "b"填的是{1} "c"
   ...: 填的是2
Out[2]: 'abcba'

In [3]: 

In [3]: # 关键字参数

In [4]: "{var1}{var2}{var3}{var2}{var1}".format(var1="a",var2="b",var3="c")
Out[4]: 'abcba'

In [5]: 

In [5]: # 混合

In [6]: "{0}{var1}{var2}".format("a",var1="b",var2="c")  # 可以这么做，但不推荐
Out[6]: 'abc'

In [7]: 

In [7]: "{var}{0}".format("a",var="b")
Out[7]: 'ba'

In [8]: exit
(py37) coder@Ubuntu:~$ source deactivate
coder@Ubuntu:~$ 

 

more knowledge

    def format(self, *args, **kwargs): # known special case of str.format
        """
        S.format(*args, **kwargs) -> str

        Return a formatted version of S, using substitutions from args and kwargs.
        The substitutions are identified by braces ('{' and '}').
        """
        pass

 

coder@Ubuntu:~$ source activate py37
(py37) coder@Ubuntu:~$ ipython
Python 3.7.0 (default, Jun 28 2018, 13:15:42)
Type 'copyright', 'credits' or 'license' for more information
IPython 6.5.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: # 错误的示范

In [2]: "{var}{0}".format(var="b","a")
  File "<ipython-input-2-ec3e374dcf52>", line 1
    "{var}{0}".format(var="b","a")
                             ^
SyntaxError: positional argument follows keyword argument

In [3]: exit
(py37) coder@Ubuntu:~$ source deactivate
coder@Ubuntu:~$ 

 

resource

• [文档] docs.python.org/3
• [规范] www.python.org/dev/peps/pep-0008
• [规范] zh-google-styleguide.readthedocs.io/en/latest/google-python-styleguide/python_language_rules
• [源码] www.python.org/downloads/source
• [ PEP ] www.python.org/dev/peps
• [平台] www.cnblogs.com
• [平台] gitee.com

 

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