PythonLearnPartMore_InfoContentList1.PythonIntroduce1.1pythonREPL1.2pythonhelloworld.py1.3
Python Learn Part
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1. Python Introduce
python 少有的一种可以称得上即简单又功能强大的编程语言
python 代表简单主义思想的语言
➜ python git:(master) python -V
Python 2.7.10
➜ python git:(master)
1.1 python REPL
➜ python git:(master) python
Python 2.7.10 (default, Jul 14 2015, 19:46:27)
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.39)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 2**3 or pow(2, 3)
8
>>> x = input("x:")
x:5
>>> print "hello ", x
hello 5
>>> print 3
3
>>> print '3'
3
>>> 0xAF
175
>>> 010
8
>>> round(1.0/3.0) #四舍五入
0.0
>>> round(1.0/2.0)
1.0
>>> import math
>>> math.floor(32.9)
32.0
>>> print r'C:\nowhere''\\' # 解决最后一个字符是 '\' 的情况！ 完美解决
C:\nowhere\
>>> print u'hello, world' # Unicode 字符串， 在python3.0中，所有的字符串都是 Unicode 字符串
hello, world
>>>
1.2 python helloworld.py
#!/usr/bin/python
# Filename : helloworld.py
print 'Hello World'
1.3 python help()
>>> help()
Welcome to Python 2.7! This is the online help utility.
help> input
Help on built-in function input in module __builtin__:
input(...)
input([prompt]) -> value
Equivalent to eval(raw_input(prompt)).
(END)
1.4 to python_string
>>> '"hello world" she said'
'"hello world" she said'
>>> "hello world"
'hello world'
>>> 10000L
10000L
>>> print "hello world"
hello world
>>> print 10000L
10000
>>> print str("Hello world")
Hello world
>>> print str(10000L)
10000
1.5 input and raw_input
>>> raw_input("shuru : ")
shuru : 6
'6'
>>> input("shuru : ") #默认为合法的python表达式
shuru : 5
5 2. Python Preliminary program
>>> i = 5
>>> i = i + 1
>>> print \
... i
6
>>> print i
6
>>>
2.1 Operators and Expression
operator precedence
Expression
#!/usr/bin/python
# Filename: expression.py
length = 5
breadth = 2
area = length * breadth
print 'Area is', area
print 'Perimeter is', 2 * (length + breadth)
2.2 python control flow
#!/usr/bin/python
# Filename: while.py
number = 23
running = True
while running:
guess = int(raw_input('Enter an integer : '))
if guess == number:
print 'Congratulations, you guessed it.'
running = False # this causes the while loop to stop
elif guess print 'No, it is a little higher than that'
else:
print 'No, it is a little lower than that'
else:
print 'The while loop is over.'
# Do anything else you want to do here
print 'Done'
break, continue
#!/usr/bin/python
# Filename: continue.py
while True:
s = raw_input('Enter something : ')
if s == 'quit':
break
if len(s) <3:
continue
print 'Input is of sufficient length'
# Do other kinds of processing here...3. function
3.1 local var
#!/usr/bin/python
# Filename: func_local.py
def func(x):
print 'x is', x
x = 2
print 'Changed local x to', x
x = 50
func(x)
print 'x is still', x
Output
$ python func_local.py
x is 50
Changed local x to 2
x is still 50
3.2 global var
#!/usr/bin/python
# Filename: func_global.py
def func():
global x
print 'x is', x
x = 2
print 'Changed local x to', x
x = 50
func()
print 'Value of x is', x
Output
$ python func_global.py
x is 50
Changed global x to 2
Value of x is 2
3.3 func_key
#!/usr/bin/python
# Filename: func_key.py
def func(a, b=5, c=10):
print 'a is', a, 'and b is', b, 'and c is', c
func(3, 7)
func(25, c=24)
func(c=50, a=100)
Output
$ python func_key.py
a is 3 and b is 7 and c is 10
a is 25 and b is 5 and c is 24
a is 100 and b is 5 and c is 50
3.4 DocStrings
# #!/usr/bin/python
# Filename: func_doc.py
def printMax(x, y):
'''Prints the maximum of two numbers.
The two values must be integers.'''
x = int(x) # convert to integers, if possible
y = int(y)
if x > y:
print x, 'is maximum'
else:
print y, 'is maximum'
return y
printMax(3, 5)
print printMax.__doc__
output
$ python func_doc.py
5 is maximum
Prints the maximum of two numbers.
The two values must be integers.4. Module
4.1 sys 模块
#!/usr/bin/python
# Filename: using_sys.py
import sys
print 'The command line arguments are:'
for i in sys.argv:
print i
print '\n\nThe PYTHONPATH is', sys.path, '\n'
4.2 from..import
yourself module
#!/usr/bin/python
# Filename: mymodule.py
def sayhi():
print 'Hi, this is mymodule speaking.'
version = '0.1'
# End of mymodule.py
mymodule_demo.py
#!/usr/bin/python
# Filename: mymodule_demo.py
import mymodule
mymodule.sayhi()
print 'Version', mymodule.version
from..import..
#!/usr/bin/python
# Filename: mymodule_demo2.py
from mymodule import sayhi, version
# Alternative:
# from mymodule import *
sayhi()
print 'Version', version
4.3 __name__
#!/usr/bin/python
# Filename: using_name.py
if __name__ == '__main__':
print 'This program is being run by itself'
else:
print 'I am being imported from another module'
每个Python模块都有它的__name__，如果它是&＃8217;__main__&＃8217;，这说明这个模块被用户单独运行，我们可以进行相应的恰当操作。
4.4 dir()
$ python
>>> import sys
>>> dir(sys) # get list of attributes for sys module
['__displayhook__', '__doc__', '__excepthook__', '__name__', '__stderr__',
'__stdin__', '__stdout__', '_getframe', 'api_version', 'argv',
'builtin_module_names', 'byteorder', 'call_tracing', 'callstats',
'copyright', 'displayhook', 'exc_clear', 'exc_info', 'exc_type',
'excepthook', 'exec_prefix', 'executable', 'exit', 'getcheckinterval',
'getdefaultencoding', 'getdlopenflags', 'getfilesystemencoding',
'getrecursionlimit', 'getrefcount', 'hexversion', 'maxint', 'maxunicode',
'meta_path','modules', 'path', 'path_hooks', 'path_importer_cache',
'platform', 'prefix', 'ps1', 'ps2', 'setcheckinterval', 'setdlopenflags',
'setprofile', 'setrecursionlimit', 'settrace', 'stderr', 'stdin', 'stdout',
'version', 'version_info', 'warnoptions']
>>> dir() # get list of attributes for current module
['__builtins__', '__doc__', '__name__', 'sys']
>>>
>>> a = 5 # create a new variable 'a'
>>> dir()
['__builtins__', '__doc__', '__name__', 'a', 'sys']
>>>
>>> del a # delete/remove a name
>>>
>>> dir()
['__builtins__', '__doc__', '__name__', 'sys']
>>>
输入的sys模块上使用dir。我们看到它包含一个庞大的属性列表。
dir() , 默认地，它返回当前模块的属性列表。
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