Python笔记
(→Format) |
(→Format) |
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第142行: | 第142行: | ||
Jack wrote Hello world | Jack wrote Hello world | ||
</source> | </source> | ||
+ | |||
+ | |||
+ | <source lang=bash> | ||
+ | Python 2.7.9 (default, Mar 1 2015, 12:57:24) | ||
+ | >>> print "%.3s " % ("jcodeer") #precise = 3 | ||
+ | jco | ||
+ | >>> print "%.*s" % (4,"jcodeer") #precise = 4 | ||
+ | jcod | ||
+ | >>> print "%10.3s" % ("jcodeer") #width = 10,precise = 3 | ||
+ | jco | ||
+ | >>> | ||
+ | </source> | ||
+ | |||
2017年5月25日 (四) 18:34的版本
目录 |
1 Quick Start
Install python2.7 from https://www.python.org/downloads/
Install pip:
$ curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py $ sudo python get-pip.py
Using the pip to install the numpy and tensorflow package:
$ sudo pip install numpy $ sudo pip install tensorflow
2 Basics
2.1 Numbers
Python 2.7.9 (default, Mar 1 2015, 12:57:24) >>> a = 3.23 >>> b = 4 >>> c = 52.3E-4 >>> print a, b, c 3.23 4 0.00523
2.2 Strings
#!/usr/bin/python str_1 = 'Jack Tan' str_2 = "Ga Xiao Duo" str_3 = '''This is a multi-line string. first line. second line''' # using the startswith method of the string object if str_1.startswith('Ja'): print("Yes, str_1 start with 'Ja'") if 'a' in str_1: print('Yes, str_1 contains the string "a"') substr = 'ac' if str_1.find(substr) != -1: print('Yes, str_1 contains the string "{0}"'.format(substr)) print('Yes, {0} contains the string "{1}"'.format('str_1', substr)) print('Yes, {} contains the string "{}"'.format('str_1', substr)) # using the format method of the string object deli = '_*_' mylist = ['Brazil', 'Russia', 'India', 'China'] # using the join method of the string object print(deli.join(mylist))
Output:
Yes, name start with 'Ja' Yes, name contains the string "a" Yes, name contains the string "ac" Brazil_*_Russia_*_India_*_China
Once your have created a string, you cannot change it
2.3 Variable
Python refers to anything used in a program as an object.
Do not need type declaration of variable in python
Python 2.7.9 (default, Mar 1 2015, 12:57:24) >>> a = 3.1415 >>> b = 100000 >>> c = 'Jack Tan' >>> d = ['x1', 'x2'] >>> print a, b, c, d 3.1415 100000 Jack Tan ['x1', 'x2'].
Variables can hold values of different types called data types. The basic types are numbers and strings. We can create our own types using classes.
2.4 Indentation
Whitespace at the beginning of the line is important!
Spaces and tabs at the beginning of the logical line are used to determine the indentation level of the logical line, which in turn is used to determine the grouping of statements.
Statements which go together must have the same indentation. Each usch set of statements is called a block
2.5 Format
#!/usr/bin/python #width = 10,precise = 3,align = left print "PI = %10.3f" %(math.pi) # don't add the '\n' at the end of line print "PI = %10.3f" %(math.pi), #width = 10,precise = 3,align = rigth print "PI = %-10.3f" % math.pi print('{0:.3}'.format(0.3333333)) #print('{0:.3}'.format(1/3)) print('{0:_^11}'.format('Hello')) print('{0:+^11}'.format('Hello')) print('{name} wrote {book}'.format(name='Jack', book='Hello world'))
Output:
PI = 3.141593 PI = 3.142 0.333 ___Hello___ +++Hello+++ Jack wrote Hello world
Python 2.7.9 (default, Mar 1 2015, 12:57:24) >>> print "%.3s " % ("jcodeer") #precise = 3 jco >>> print "%.*s" % (4,"jcodeer") #precise = 4 jcod >>> print "%10.3s" % ("jcodeer") #width = 10,precise = 3 jco >>>
formatter = "%r %r %r %r" print formatter % (1, 2, 3, 4) print formatter % ("one", "two", "three", "four") print formatter % (True, False, False, True)
1 2 3 4 'one' 'two' 'three' 'four' True False False True
3 Operators
4 Control Flow
5 Functions
6 Data Structures
7 Exceptions
7.1 with...as
#!/usr/bin/python import sys class test: def __enter__(self): print("enter") return 1 def __exit__(self, *args): print("clean up") return False #return True with test() as t: print("t is not the result of test(), it's __enter__ returned") print("t is 1, yes, it's {0}".format(t)) print "t is 1, yes, it's", t raise NameError("Error") sys.exit() print("Never here")
8 Modules
9 Object Oriented
10 Resource
- Online Python: http://www.compileonline.com/execute_python_online.php
- Python Quick Start: http://www.tutorialspoint.com/python/python_lists.htm