Lesson Three: Python basic data Type lectures (3/3)

One, type
1. Immutable type string, int, tuple
2. Variable Type list, Dict

>>> a = "test"
>>> A[0]
' t '
>>> a[0]=e
Traceback (most recent):
File "<stdin>", line 1, in <module>
Nameerror:name ' e ' is not defined
>>> a = ["T", "E", "s", "T"]
>>> A[0]
' t '
>>> a[0]= "E"
>>> A
[' E ', ' e ', ' s ', ' t ']

Second, to investigate the string
What exactly is a sequence? The Eagle and the chick
1. The difference between three symbols "," "," "" "" ""
Print "This is 1 '"
print ' This is 2 '
Print "" "
' This is 1 '
"This is 2 '"
"""
2. Offset starting from 0
3. How to change the string's replace find

From the following statement, we want to know that a will not change after a.replace, if the need to change the value must be assigned value.

>>> A = "This is the world"
>>> A.replace ("This", "that")
' That's world '
>>> A
' This was World '
>>> a = A.replace ("This", "that")
>>> A
' That's world '
>>> A.find ("World")
8
>>> a.find ("www")
-1
>>> A[8]
' W '
>>> A[8:]
' World '

What should I do if we match multiple values?
>>> Help (A.find)
Help on built-in function find:

Find (...)
S.find (Sub [, Start [, end]]) int

Return the lowest index in S where substring sub is found,
such that sub is contained within S[start:end]. Optional
Arguments start and end is interpreted as in slice notation.

Return-1 on failure.

>>> a = "World, World, World"
>>> A.find ("World")
0
>>> A.find ("World", 11)
14

Third, the format of the scrutiny
1.% formatting method (placeholder)

>>> a = "World, World, World"
>>> A.find ("World")
0
>>> A.find ("World", 11)
14
>>> A = "This is a%s%s"% (4, 10)
>>> Print a
This is a 4 10

2. Format Formatting method

Call mode B = "This is {} {}". Format ("Apple", "my")
Location mode B = "This is {1} {0}". Format ("Apple", "my")
Identifier mode B = "This is {whose} {fruit}". Format (fruit = "Apple", whose = "my")

3. Why use Format
4. There is another way, the dictionary comes

A = "This is% (whose) s% (fruit) s"% {' whose ': ' Apple ', ' fruit ': ' My '}

Iv. further discussion open file

Close the file after you have written the file.
A = open ("Tmp1.txt", "W")
A.write ("This is a Apple")
A.close ()

To open and read files between read files, assign files to variables
A = open ("Tmp1.txt", "R")
A.read (20)
A.seek (0)
A.read (20)

Standard library Introduction Linecache

>>> a.write ("HAHA\NHAHA\NSFASDDA\NSDFSA")
>>> A.close ()
>>> Import Linecache
>>> print Linecache.getline ("Tmp2.txt", 1)
haha

>>> print Linecache.getline ("Tmp2.txt", 2)
haha

>>> print Linecache.getline ("Tmp2.txt", 3)
Sfasdda

>>> print Linecache.getline ("Tmp2.txt", 4)
Sdfsa

>>> lines = Linecache.getlines ("Tmp2.txt")
>>> Print Lines
[' haha\n ', ' haha\n ', ' sfasdda\n ', ' sdfsa\n ']
>>> Help (Linecache)
NAME
Linecache-cache lines from files.

FILE
d:\python27\lib\linecache.py

DESCRIPTION
This is intended to read lines from modules imported--hence if a filename
is not found, it would look down the module search path for a file by
That name.

FUNCTIONS
Checkcache (Filename=none)
Discard cache entries that is out of date.
(This isn't checked upon each call!)

ClearCache ()
Clear the cache entirely.

Getline (filename, Lineno, Module_globals=none)

DATA
__all__ = [' getline ', ' clearcache ', ' Checkcache ']

You can view the source code,

Look at the source code, in fact, is quite simple. Do not fear, nothing can not understand, once fear will produce a sense of distance.
Practice more, not optical theory. Bite the bullet and look at something, ask more questions. (the teacher said that this sentence I still very much agree with)

Lesson Three: Python basic data Type lectures (3/3)