Python very important data types: strings, lists, dictionaries, tuples, often have netizens asked them what is the important difference between them? Can you give me a few examples to illustrate the next! Let's talk about it.
Data type:
?
1 2 3 4 |
float-floating-point numbers can be accurate to 15 digits after the decimal point int-integer can be infinitely large bool-Non-zero to True, 0 is false list-list |
Float/int:
Operator:
/-Floating-point operations except
-When the result is positive, rounding; 11//5 = 2; 11//4 = 2
When the result is negative, the downward rounding; -11//5=-3; -11//4=-3
When the numerator's denominator is float, the result is float type
**-compute power; 11**2 =121
%-to take more than
Other mathematical operations:
1. Score:
Import fractions;
Fractions. Fraction (1,3) -1/3
Import Math;
-math.sin ()
-math.cos ()
-math.tan ()
-math.asin ()
math.pi-3.1415926 ...
Math.sin (MATH.PI/2)-1.0
Math.tan (MATH.PI/4)-0.9999999999 ...
Math.sin (); Math
List:
Created: A_list = [' A ', ' B ', ' Mpilgrim ', ' z ', ' example ']
a_list[-1]-' Example '
a_list[0]-' a '
a_list[1:3]-[' B ', ' Mpilgrim ', ' Z ']
A_list[:3]-[' A ', ' B ', ' Mpilgrim ']
A_list[3:]-[' z ', ' example ']
A_list[:]/a_list-[' A ', ' B ', ' Mpilgrim ', ' z ', ' example '
* Note: a_list[:] and a_list return a different list, but they have the same element
A_list[x:y]-Gets the list slice, x specifies the starting position of the first slice index, and y Specifies the slice index location that is not included in the cutoff.
To add an element to a list:
A_list = [' A ']
A_list = A_list + [2.0, 3]-[' A ', 2.0, 3]
A_list.append (True)-[' A ', 2.0, 3, True]
A_list.extend ([' Four ', ' Ω '])-[' A ', 2.0, 3, True, ' Four ', ' Ω ']
A_list.insert (0, ' ω ')-[' ω ', ' a ', 2.0, 3, True, ' Four ', ' Ω ']
List Other Features:
A_list = [' A ', ' B ', ' new ', ' Mpilgrim ', ' new ']
A_list.count (' new ')-2
A_list.count (' Mpilgrim ')-1
' New ' in A_list-true
A_list.index (' new ')-2
A_list.index (' Mpilgrim ')-3
A_list.index (' C ')-through a exception because ' C ' isn't in a_list.
Del a_list[1]-[' A ', ' new ', ' Mpilgrim ', ' new '
A_list.remove (' new ')-[' a ', Mpilgrim ', ' new '
Note: Remove deletes only the first ' new '
A_list.pop ()-' new '/[' a ', Mpilgrim '] (delete and return the last element)
A_list.pop (0)-' a '/[' Mpilgrim '] (delete and return No. 0 Element)
The empty list is false and the other list is true.
Tuples (elements are immutable lists):
Definition: Same as the definition of a list, except for the collection of the entire element with parentheses, not square brackets closed
A_tuple = ("A", "B", "Mpilgrim", "Z", "example")
A_tuple = (' A ', ' B ', ' Mpilgrim ', ' z ', ' example ')
Tuple can only be indexed and cannot be modified.
Advantages of tuples in relation to lists:
1. Fast speed
2. "Write protection", more secure
3. Some tuples can be used as dictionary keys??
The built-in tuple () function takes a list parameter and converts the list into tuples
Similarly, the list () function converts a tuple to a list
Assign multiple values at the same time:
v = (' A ', 2, True)
(x,y,z) = V-x= ' A ', y=2, z=true
Range ()-built-in function to assign values to continuous variables
(Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday) = range (7)
Monday-0
Thursday-3
Sunday-6
Range ()-The built-in function range () builds an integer sequence in which the range () function returns an iterator.
Collection (the value inside is unordered):
Create collections: Separate each value with commas, and include all values with braces {}.
A_set = {1}
Type (A_set)-
To create a collection based on a list:
A_list = [' A ', ' B ', ' Mpilgrim ', True, False, 42]
A_set = Set (A_list)
A_set-{' A ', ' B ', ' Mpilgrim ', True, False, 42}
A_set = set ()-Gets an empty set
A_dic = {An empty DIC is obtained
To modify a collection:
A_set = {1,2}
A_set.add (4)-{1,2,4}
Len (A_set)-3
A_set.add (1)-{1,2,4}
A_set.update ({2,4,6})-{1,2,4,6}
A_set.update ({3,6,9}, {1,2,3,5,8,13})-{1,2,3,4,5,6,8,9,13}
A_set.update ([15,16])-{1,2,3,4,5,6,8,9,13,15,16}
A_set.discard (16)-{1,2,3,4,5,6,8,9,13,15}
A_set.discard (16)-{1,2,3,4,5,6,8,9,13,15}
A_set.remove (15)-{1,2,3,4,5,6,8,9,13}
A_set.remove ()-through a exception
A_set.pop ()-return 1/{2,3,4,5,6,8,9,13}
Note: A_set.pop () randomly deletes a value from the collection and returns the value.
A_set.clear ()-set ()
A_set.pop ()-through exception.
Other operations for the collection:
A_set = {2,3,4,5,6,8,9,13}
In A_set-false
4 in A_set-true
B_set = {3,4,10,12}
A_set.union (B_set)-two sets of and
A_set.intersetion (B_set)-intersection of two sets
A_set.difference (B_set)-a_set with elements that are not in B_set
A_set.symmetric_difference (B_set)-Returns all elements that appear in only one collection
A_set.issubset (B_set)-Determine if A_set is a subset of B_set
B_set.issuperset (A_set)-Determine if B_set is a superset of A_set
In a Boolean-type context, the empty collection is false, and any collection that contains more than one element is true.
Dictionary (unordered collection of key-value pairs):
To create a dictionary:
A_dic = {' Server ': ' db.diveintopython3.org ',
' Databas ': ' MySQL '}
a_dic[' server ']-' db.diveintopython3.org '
a_dic[' database ']-' MySQL '
To modify a dictionary:
a_dic[' user ' = ' mark '-{' user ': ' Mark ', ' Server ': ' db.diveintopython3.org ', ' Database ': ' Blog '}
a_dic[' database ' = ' blog '-{' user ': ' Mark ', ' Server ': ' db.diveintopython3.org ', ' Database ': ' Blog '}
a_dic[' user ' = ' bob '-{' user ': ' Bob ', ' Server ': ' db.diveintopython3.org ', ' Database ': ' Blog '}
a_dic[' user ' = ' mark '-{' user ': ' Bob ', ' uuser ': ' Mark ', ' Server ': ' db.diveintopython3.org ', ' Database ': ' Blog '}
Note: 1. Duplicate keys are not allowed in the dictionary. Assigning values to an existing key will overwrite the original value;
2. You can add a new key value pair at any time;
3. Dictionary keys are case-sensitive.
Mixed Value Dictionary:
suffixes = {1000:[' KB ', ' MB ', ' GB ', ' TB ', ' PB ', ' EB ', ' ZB ', ' YB '],
1024: [' KiB ', ' MiB ', ' GiB ', ' TiB ', ' PiB ', ' EiB ', ' ZiB ', ' Yib ']}
Len (suffixes)-2
1000 in Suffixes-true
suffixes[1024]-[' KiB ', ' MiB ', ' GiB ', ' TiB ', ' PiB ', ' EiB ', ' ZiB ', ' Yib '
suffixes[1000][3]-' TB '
Empty dictionary is false, all other dictionaries are true
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