Cloud Classroom-python Learning notes (7)

First, the dictionary

1. What is a dictionary

1. A series of key-value (Key-value) pairs
2. Find the corresponding "value" by "key"
3, similar to the paper dictionary, through the Word Index table to find its corresponding definition
C++:map, java:hashtable or HashMap
Example: Phone book

2. Create a dictionary

Use {} to create a dictionary

Use: Specify key: Value pair
my_dict={' John ': 86411234, ' Bob ': 24896880, ' Mike ': 354859977}

3. Access to the dictionary
Using the [] operator, the key as the index
Add a new pair of

 1  my_dict={ " john   ": 86411234,"   Bob  : 24896880,"  mike  : 354859977 2  print  my_dict[ " john   " ]   my_dict[ " tom   ' ] = 98644336794  print  my_dict 

4. Dictionary operators and methods

1 len (my_dict): Number of key- value pairs in a dictionary 2 in my_dict: Quickly determine if key is a key in the dictionary: Time Complexity O (1)3  equivalent to My_dict.has_key (key)4 for in my_dict: The key in the enumeration dictionary, note: The key is unordered

More ways:

1 my_dict.items (): All keys- value pairs 2My_dict.keys (): All keys 3My_ Dict.values (): Full value 4 my_dict.clear (): Empty dictionary

5. Example 1: Read a string to calculate the number of occurrences of each letter

Scenario One: Generate 26 variables representing the number of letters appearing

Scenario Two: Generate a list of 26 elements, converting each letter to the index value of the object

1 ' Abdddeyyyrewgq ' 2 lst = [0]*263 for in s:4     Lst[ord (i) -97] +=15     6print LST

Scenario Three: Generate a dictionary, the letter to do the key, corresponding to the number of occurrences of the value

s =={} for in s:    if in D:        + = 1    Else :         = 1    print D

Example 2: Read a novel emma.txt, print the first 10 most common words

1F= Open ('Emma.txt')2Word_freq = {}3  forLineinchF:4Words =Line.strip (). Split ()5      forWordinchwords:6         ifWordinchWord_freq:7Word_freq[word] + = 18         Else:9Word_freq[word] = 1Ten              OneFreq_word = [] A  forWord,freqinchWord_freq.items (): - Freq_word.append ((Freq,word)) -Freq_word.sort (reverse =True) the  -  forFreq,wordinchFreq_word[:10]: -     PrintWord -F.close ()

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Example 3: Flipping a dictionary: generating a new dictionary whose key is the value of the original dictionary with the key of the original dictionary

1D1 = {'Zhang': 123,'Wang': 456,'Li': 123,'Zhao': 456}2D2 = {}3  forName,roominchD1.items ():4     ifTheinchD2:5 d2[room].append (name)6     Else :7D2[room] =[Name]8 PrintD2

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Two, set (set)

1, set: unordered element set, similar to dictionary, but no value
2. Create:
x = Set ()
X={key1,key2,....}
3. Add and remove
X.add (' body '
X.remove (' body ')
4, set of operators:
-: Difference Set
&: Intersection
|: and set
！ =: Not equal to
= =: equals
In: Members
For key in set: enumeration
5. Example: Chinese participle
I/Love/Beijing/Tiananmen
Algorithm: Forward maximum match
Take long words from left to right

1 defload_dict (filename):2Word_dict =set ()3Max_len = 14f =open (filename)5      forLineinchF:6Word = Unicode (Line.strip (),'Utf-8')7 Word_dict.add (Word)8         ifLen (word) >Max_len:9Max_len =len (Word)Ten     returnmax_len,word_dict One  A deffmm_word_seg (sent,max_len,word_dict): -Begin =0 -Words = [] theSent = Unicode (Sent,'Utf-8') -      -      whileBegin <Len (Sent): -          forEndinchRange (begin + Max_len,begin,-1): +             ifSent[begin:end]inchword_dict: - words.append (Sent[begin:end]) +                  Break ABegin =End at     returnwords -Max_len,word_dict = Load_dict ('Lexicon.dic') -  -Sent = Raw_input ('Input a sententce:') -Words =fmm_word_seg (sent,max_len,word_dict) -  forWordinchwords: in     PrintWord

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Cloud Classroom-python Learning notes (7)