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Python基础（函数-递归）

2018-02-10 14:41 447 查看

本章内容：

深浅拷贝
函数（全局与局部变量）
内置函数
文件处理
三元运算
lambda 表达式
递归（斐波那契数列）
冒泡排序

深浅拷贝

一、数字和字符串

对于数字和字符串而言，赋值、浅拷贝和深拷贝无意义，因为其永远指向同一个内存地址。

#定义函数
#n 叫做函数 name 的形式参数，简称：形参

def name(n):
print(n)

#执行函数
#'nick' 叫做函数 name 的实际参数，简称：实参

name('nick')

def func(name, age = 18):
print("%s:%s")%(name,age)

# 指定参数
func('nick', 19)
# 使用默认参数
func('nick')

注：默认参数需要放在参数列表最后

def func(*args):
print args

# 执行方式一
func(11,22,33,55,66)

# 执行方式二
li = [11,22,33,55,66]
func(*li)

def func(**kwargs):
print kwargs

# 执行方式一
func(name＝'nick',age=18)

# 执行方式二
li = {'name':'nick', age:18, 'job':'pythoner'}
func(**li)

def hi(a,*args,**kwargs):
print(a,type(a))
print(args,type(args))
print(kwargs,type(kwargs))
hi(11,22,33,k1='nick',k2='jenny')

#发送邮件实例

def mail(主题,邮件内容='test',收件人='630571017@qq.com'):
import smtplib
from email.mime.text import MIMEText
from email.utils import formataddr

msg = MIMEText(邮件内容, 'plain', 'utf-8')
msg['From'] = formataddr(["发件人", '发件人地址'])
msg['To'] = formataddr(["收件人", '630571017@qq.com'])
msg['Subject'] = 主题

server = smtplib.SMTP("smtp.126.com", 25)
server.login("登录邮箱账号", "邮箱密码")
server.sendmail('发件邮箱地址账号', [收件人地址, ], msg.as_string())
server.quit()

mail('我是主题',收件人='630571017@qq.com',邮件内容='邮件内容')
mail(主题='我是主题',)

3、全局与局部变量

全局变量在函数里可以随便调用，但要修改就必须用 global 声明

内置函数

zip函数接受任意多个（包括0个和1个）序列作为参数，返回一个tuple列表。具体意思不好用文字来表述，直接看示例：

1.示例1：

复制代码
x = [1, 2, 3]

y = [4, 5, 6]

z = [7, 8, 9]

xyz = zip(x, y, z)

print xyz
复制代码
运行的结果是：

[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

从这个结果可以看出zip函数的基本运作方式。

2.示例2：

x = [1, 2, 3]
y = [4, 5, 6, 7]
xy = zip(x, y)
print xy
运行的结果是：

[(1, 4), (2, 5), (3, 6)]

从这个结果可以看出zip函数的长度处理方式。

3.示例3：

x = [1, 2, 3]
x = zip(x)
print x
运行的结果是：

[(1,), (2,), (3,)]

从这个结果可以看出zip函数在只有一个参数时运作的方式。

4.示例4：

x = zip()
print x
运行的结果是：

[]

从这个结果可以看出zip函数在没有参数时运作的方式。

5.示例5：

复制代码
x = [1, 2, 3]

y = [4, 5, 6]

z = [7, 8, 9]

xyz = zip(x, y, z)

u = zip(*xyz)

print u
复制代码
运行的结果是：

[(1, 2, 3), (4, 5, 6), (7, 8, 9)]

一般认为这是一个unzip的过程，它的运行机制是这样的：

在运行zip(*xyz)之前，xyz的值是：[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

那么，zip(*xyz) 等价于 zip((1, 4, 7), (2, 5, 8), (3, 6, 9))

所以，运行结果是：[(1, 2, 3), (4, 5, 6), (7, 8, 9)]

注：在函数调用中使用*list/tuple的方式表示将list/tuple分开，作为位置参数传递给对应函数（前提是对应函数支持不定个数的位置参数）

6.示例6：

x = [1, 2, 3]
r = zip(* [x] * 3)
print r
运行的结果是：

[(1, 1, 1), (2, 2, 2), (3, 3, 3)]

它的运行机制是这样的：

[x]生成一个列表的列表，它只有一个元素x

[x] * 3生成一个列表的列表，它有3个元素，[x, x, x]

zip(* [x] * 3)的意思就明确了，zip(x, x, x)

文件处理

open函数，该函数用于文件处理
一、打开文件

打开文件时，需要指定文件路径和以何等方式打开文件，打开后，即可获取该文件句柄，日后通过此文件句柄对该文件操作。

打开文件的模式有：

r ，只读模式【默认】
w，只写模式【不可读；不存在则创建；存在则清空内容】
x，只写模式【不可读；不存在则创建，存在则报错】
a，追加模式【不可读；不存在则创建；存在则只追加内容】

"+" 表示可以同时读写某个文件

r+，读写【可读，可写】
w+，写读【可读，可写】
x+ ，写读【可读，可写】
a+，写读【可读，可写】

"b"表示以字节的方式操作

rb 或 r+b
wb 或 w+b
xb 或 w+b
ab 或 a+b

注：以b方式打开时，读取到的内容是字节类型，写入时也需要提供字节类型

二、操作

class file(object)
def close(self): # real signature unknown; restored from __doc__
关闭文件
"""
close() -> None or (perhaps) an integer.  Close the file.

Sets data attribute .closed to True.  A closed file cannot be used for
further I/O operations.  close() may be called more than once without
error.  Some kinds of file objects (for example, opened by popen())
may return an exit status upon closing.
"""

def fileno(self): # real signature unknown; restored from __doc__
文件描述符
"""
fileno() -> integer "file descriptor".

This is needed for lower-level file interfaces, such os.read().
"""
return 0

def flush(self): # real signature unknown; restored from __doc__
刷新文件内部缓冲区
""" flush() -> None.  Flush the internal I/O buffer. """
pass

def isatty(self): # real signature unknown; restored from __doc__
判断文件是否是同意tty设备
""" isatty() -> true or false.  True if the file is connected to a tty device. """
return False

def next(self): # real signature unknown; restored from __doc__
获取下一行数据，不存在，则报错
""" x.next() -> the next value, or raise StopIteration """
pass

def read(self, size=None): # real signature unknown; restored from __doc__
读取指定字节数据
"""
read([size]) -> read at most size bytes, returned as a string.

If the size argument is negative or omitted, read until EOF is reached.
Notice that when in non-blocking mode, less data than what was requested
may be returned, even if no size parameter was given.
"""
pass

def readinto(self): # real signature unknown; restored from __doc__
读取到缓冲区，不要用，将被遗弃
""" readinto() -> Undocumented.  Don't use this; it may go away. """
pass

def readline(self, size=None): # real signature unknown; restored from __doc__
仅读取一行数据
"""
readline([size]) -> next line from the file, as a string.

Retain newline.  A non-negative size argument limits the maximum
number of bytes to return (an incomplete line may be returned then).
Return an empty string at EOF.
"""
pass

def readlines(self, size=None): # real signature unknown; restored from __doc__
读取所有数据，并根据换行保存值列表
"""
readlines([size]) -> list of strings, each a line from the file.

Call readline() repeatedly and return a list of the lines so read.
The optional size argument, if given, is an approximate bound on the
total number of bytes in the lines returned.
"""
return []

def seek(self, offset, whence=None): # real signature unknown; restored from __doc__
指定文件中指针位置
"""
seek(offset[, whence]) -> None.  Move to new file position.

Argument offset is a byte count.  Optional argument whence defaults to
(offset from start of file, offset should be >= 0); other values are 1
(move relative to current position, positive or negative), and 2 (move
relative to end of file, usually negative, although many platforms allow
seeking beyond the end of a file).  If the file is opened in text mode,
only offsets returned by tell() are legal.  Use of other offsets causes
undefined behavior.
Note that not all file objects are seekable.
"""
pass

def tell(self): # real signature unknown; restored from __doc__
获取当前指针位置
""" tell() -> current file position, an integer (may be a long integer). """
pass

def truncate(self, size=None): # real signature unknown; restored from __doc__
截断数据，仅保留指定之前数据
"""
truncate([size]) -> None.  Truncate the file to at most size bytes.

Size defaults to the current file position, as returned by tell().
"""
pass

def write(self, p_str): # real signature unknown; restored from __doc__
写内容
"""
write(str) -> None.  Write string str to file.

Note that due to buffering, flush() or close() may be needed before
the file on disk reflects the data written.
"""
pass

def writelines(self, sequence_of_strings): # real signature unknown; restored from __doc__
将一个字符串列表写入文件
"""
writelines(sequence_of_strings) -> None.  Write the strings to the file.

Note that newlines are not added.  The sequence can be any iterable object
producing strings. This is equivalent to calling write() for each string.
"""
pass

def xreadlines(self): # real signature unknown; restored from __doc__
可用于逐行读取文件，非全部
"""
xreadlines() -> returns self.

For backward compatibility. File objects now include the performance
optimizations previously implemented in the xreadlines module.
"""
pass

class TextIOWrapper(_TextIOBase):
"""
Character and line based layer over a BufferedIOBase object, buffer.

encoding gives the name of the encoding that the stream will be
decoded or encoded with. It defaults to locale.getpreferredencoding(False).

errors determines the strictness of encoding and decoding (see
help(codecs.Codec) or the documentation for codecs.register) and
defaults to "strict".

newline controls how line endings are handled. It can be None, '',
'\n', '\r', and '\r\n'.  It works as follows:

* On input, if newline is None, universal newlines mode is
enabled. Lines in the input can end in '\n', '\r', or '\r\n', and
these are translated into '\n' before being returned to the
caller. If it is '', universal newline mode is enabled, but line
endings are returned to the caller untranslated. If it has any of
the other legal values, input lines are only terminated by the given
string, and the line ending is returned to the caller untranslated.

* On output, if newline is None, any '\n' characters written are
translated to the system default line separator, os.linesep. If
newline is '' or '\n', no translation takes place. If newline is any
of the other legal values, any '\n' characters written are translated
to the given string.

If line_buffering is True, a call to flush is implied when a call to
write contains a newline character.
"""
def close(self, *args, **kwargs): # real signature unknown
关闭文件
pass

def fileno(self, *args, **kwargs): # real signature unknown
文件描述符
pass

def flush(self, *args, **kwargs): # real signature unknown
刷新文件内部缓冲区
pass

def isatty(self, *args, **kwargs): # real signature unknown
判断文件是否是同意tty设备
pass

def read(self, *args, **kwargs): # real signature unknown
读取指定字节数据
pass

def readable(self, *args, **kwargs): # real signature unknown
是否可读
pass

def readline(self, *args, **kwargs): # real signature unknown
仅读取一行数据
pass

def seek(self, *args, **kwargs): # real signature unknown
指定文件中指针位置
pass

def seekable(self, *args, **kwargs): # real signature unknown
指针是否可操作
pass

def tell(self, *args, **kwargs): # real signature unknown
获取指针位置
pass

def truncate(self, *args, **kwargs): # real signature unknown
截断数据，仅保留指定之前数据
pass

def writable(self, *args, **kwargs): # real signature unknown
是否可写
pass

def write(self, *args, **kwargs): # real signature unknown
写内容
pass

def __getstate__(self, *args, **kwargs): # real signature unknown
pass

def __init__(self, *args, **kwargs): # real signature unknown
pass

@staticmethod # known case of __new__
def __new__(*args, **kwargs): # real signature unknown
""" Create and return a new object.  See help(type) for accurate signature. """
pass

def __next__(self, *args, **kwargs): # real signature unknown
""" Implement next(self). """
pass

def __repr__(self, *args, **kwargs): # real signature unknown
""" Return repr(self). """
pass

buffer = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

closed = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

encoding = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

errors = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

line_buffering = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

name = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

newlines = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

_CHUNK_SIZE = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

_finalizing = property(lambda self: object(), lambda self, v: None, lambda self: None)  # default

三、管理上下文

为了避免打开文件后忘记关闭，可以通过管理上下文，即：

如此方式，当with代码块执行完毕时，内部会自动关闭并释放文件资源。

在Python 2.7 及以后，with又支持同时对多个文件的上下文进行管理，即：