Python list of list dictionary of dict string of string basic operation summary

Create a list of

sample_list = ['a',1,('a','b')]

Python list operation

sample_list = ['a','b',0,1,3]

I get some value in the list

value_start = sample_list[0]

end_value = sample_list[-1]

Deletes the first value in the list

del sample_list[0]

Insert a value in the list

sample_list[0:0] = ['sample value']

I get the length of the list

list_length = len(sample_list)

List traversal

for element in sample_list:

    print 'element' 

   
Python lists advanced operations/tricks

Produces a list of increasing values

num_inc_list = range(30)

#will return a list [0,1,2,...,29]

Initializes the list with a fixed value

initial_value = 0

list_length = 5

sample_list = [ initial_value for i in range(10)]

sample_list = [initial_value]*list_length

# sample_list ==[0,0,0,0,0]

Attachment: python built-in types

1. List: list (that is, dynamic array, vector of C++ standard library, but can contain different types of elements in a list)
A = [" I "and" you "and" he "and" she "]           The # element can be of any type.

Subscript: read and write by subscript as an array
Starting at 0, there is the use of negative subscripts
0 the first element, minus 1 the last element,
Minus len first element, len minus 1 last element
Take the number of elements in list

len(list)   #list The length of the. The method actually invokes this object __len__(self) Methods.  

Create a continuous list

L = range(1,5)      # namely  L=[1,2,3,4], There is no last element 

L = range(1, 10, 2) # namely  L=[1, 3, 5, 7, 9]

The list of methods

L.append(var)   # Additional elements 

L.insert(index,var)

L.pop(var)      # Returns the last element, and from list To remove the 

L.remove(var)   # Delete the element that first appears 

L.count(var)    # The number of occurrences of this element in the list 

L.index(var)    # The location of the element , No exception is thrown  

L.extend(list)  # additional list , namely the merger list to L on 

L.sort()        # The sorting 

L.reverse()     # Reverse order 

list  The operator :,+,* , the key word del

a[1:]       # Fragment operator for children list The extraction of the 

[1,2]+[3,4] # for [1,2,3,4] . with extend()

[2]*4       # for [2,2,2,2]

del L[1]    # Deletes the element with the specified index 

del L[1:3]  # Deletes an element with the specified subscript range 

The list of the copy

L1 = L      #L1 for L Alias, with C That's the same address, right L1 Operation of L Operation. This is how the function argument is passed 

L1 = L[:]   #L1 for L Is another copy. 

      

list comprehension

   [ <expr1> for k in L if <expr2> ]

 

2. Dictionary (map of the C++ standard library)

dict = {'ob1':'computer', 'ob2':'mouse', 'ob3':'printer'}

Each element is a pair, containing two parts: key and value. Key is of type Integer or string, and value is of any type.
The key is unique, and the dictionary recognizes only the last key assigned.

The method of the dictionary

D.get(key, 0)       # with dict[key] , returns the default value if there is an extra no, 0 . [] No exception is thrown 

D.has_key(key)      # There is the key to return TRUE , otherwise, FALSE

D.keys()            # Returns a list of dictionary keys 

D.values()          # Returns a list of values from a dictionary that can contain duplicate elements 

D.items()           # Returns all dictionary entries in a list, each of which is derived from ( key , value ), But the items are returned in no particular order         
D.update(dict2)     # Add merge dictionary 

D.popitem()         # To get a pair And remove it from the dictionary. Empty throws exception 

D.clear()           # Empty the dictionary, same del dict

D.copy()            # Copy a dictionary 

D.cmp(dict1,dict2)  # Compare dictionaries, ( Priority is the number of elements, key size, key value size )

                    # The first big return 1 , little return -1 , same return 0

            

dictionary The copy 

dict1 = dict        # The alias 

dict2=dict.copy()   # Clone, another copy. 

3. Tuple: a tuple (that is, an array of constants)

tuple = ('a', 'b', 'c', 'd', 'e')

The [],: operators of list can be used to extract elements. You just can't modify elements directly.

4, the string:         String (that is, list of characters that cannot be modified)

str = "Hello My friend"

The string is a whole. If you want to modify a part of the string directly, that's not possible. But we can read some part of the string.
Extraction of substrings

str[:6]

The string contains the judgment operators: in, not in

"He" in str

"she" not in str

The string module also provides a number of methods, such as

S.find(substring, [start [,end]]) # Can refer to a range lookup substring, return an index value, otherwise return -1

S.rfind(substring,[start [,end]]) # Reverse lookup 

S.index(substring,[start [,end]]) # with find I just can't find it ValueError abnormal 

S.rindex(substring,[start [,end]])# Reverse the search as above 

S.count(substring,[start [,end]]) # Returns the number of substrings found 
S.lowercase()

S.capitalize()      # Capital letter 

S.lower()           # Turn to lowercase 

S.upper()           # Turn the capital 

S.swapcase()        # Case interchange 
S.split(str, ' ')   # will string turn list , separated by Spaces 

S.join(list, ' ')   # will list turn string , connected by a space 

A built-in function that handles strings

len(str)                # The length of the string 

cmp("my friend", str)   # String comparison. The first one is big, return 1

max('abcxyz')           # Find the largest character in the string 

min('abcxyz')           # Find the smallest character in a string 

A string of conversion

            

float(str) # To float, float("1e-1")   The results for 0.1

int(str)        # To be an integer,   int("12")   The results for 12

int(str,base)   # become base Base integer, int("11",2)  The results for 2

long(str)       # It becomes a long integer, 

long(str,base)  # become base Base long integer, 

Formatting of strings (note their escape characters, mostly in C, omitted)
The str_format % (argument list) and the # argument list are defined as a tuple and cannot be changed on the fly
> > > Print ""%s's height is % DCM "% ("My brother", 180)
                  The result is shown as My brother's height is 180cm

.

Transformation of a list and a tuple

The tuple (ls)
The list (ls)