preface

Recent work and research involved in data mining and machine learning, for the purpose of inducing and summarizing knowledge to write down a series of articles, this series will include basic Python data types and data structure, function and object-oriented related knowledge, and then introduces data mining and machine learning is often used Numpy, Pandas. Hopefully, this series of articles will help anyone new to Python or data mining and machine learning.

Basic data types

digital

Python treats all numbers with a decimal point as floating point numbers, and the basic operations of addition, subtraction, multiplication and division are no different from those of other languages.

string

Python, like most languages, declares strings with “”.

poet = "We are all in the gutter, but some of us are looking for stars"
print(poet);
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Strings are whitespace sensitive and do not actively remove whitespace. We can remove strings on the left and both ends of a string by lstrip and strip.

name = " Python"
name1 = " Python "

print(name.lstrip())
print(name1.strip())
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Python also concatenates strings with +

name = "hello"+" Python"
print(name.lstrip())
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Note that Python differs from other languages such as Java in that Python does not actively convert other types to string types when concatenating strings

age = 23
message = "Happy" + age + "rd Birthday"
print(message.lstrip())

# error
TypeError: can only concatenate str (not "int") to str Traceback (most recent call last):  File "D:/Program Files/project/hello.py", line 3, in <module>  message = "Happy" + 23 + "rd Birthday" TypeError: can only concatenate str (not "int") to str  Copy the code

Must be changed to

age = 23
message = "Happy" + str(age) + "rd Birthday"
print(message.lstrip())
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The list of

A list of basic

A list is a series of elements arranged in a particular order. A list can be declared by [].

names = ["Python".'Java'.'C++']
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Python lists access and modify elements similar to data in some languages, elements are accessed and modified by subscripts starting at 0.

names[0] = 'go'
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You can use appEnd to add elements to the end of the list

names.append('C')
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Insert to insert an element at a specific location

names.insert(0, 'Ruby')
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There are several ways to remove elements from a list. You can use del to remove elements.

del names[0]
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You can also use pop to delete elements

names.pop(0)
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Remove removes an element by value. Note that remove removes only one value. If there are multiple values in the list, you need to call remove multiple times.

names.remove('Java')
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Sorting of lists: You can use sort to permanently sort the list, or you can sort backwards by passing the parameter Reverse = True.

nums = [1, 9, 7, 5, 4, 3, 2]
nums.sort(reverse=True)
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Sort changes the list permanently, and you can use sorted if you just want to sort it temporarily.

nums = [1, 9, 7, 5, 4, 3, 2]
print(sorted(nums))
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You can use reverse to reverse the list

nums = [1, 9, 7, 5, 4, 3, 2]
nums.reverse()
print(nums)
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Len can be used to get the length of the list

len(nums)
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To avoid overstepping bounds when accessing the list, Python represents the last element as -1, the second-to-last element as -2, and so on

nums[-1]
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The list of operations

We can use the for in statement to iterate over a list. Note that Python uses the: and indentation instead of the {} commonly used in other languages to represent blocks, which is also a Pyhthon feature.

names = ["Python".'Java'.'C++'.'go'.'Ruby']
for item in names:
    print(item)
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We can also use the range function to generate a list of numbers, range(1, 5) returns 1, 2, 3, 4, and range(1, 5, 2) can set the step size, range(1, 5, 2) returns 1, 3.

for i in range(1, 5, 2):
    print(i)
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You can construct a list of numbers using list plus range. You can use min, Max, and sum to find the minimum, maximum, and sum of a list of numbers.

nums = list(range(1, 5))
print(max(nums))
print(min(nums))
print(sum(nums))
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We can also create lists through list parsing, as follows, where ** in Python stands for power operation.

squares = [value**2 for value in range(1, 5)]
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Is equivalent to

squares = []
for value in range(1, 5):
    squares.append(value**2)
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Python can get a portion of a list by slicing.

names = ["Python".'Java'.'C++'.'go'.'Ruby']
print(names[1:3])
# return ['Java', 'C++']
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[1:3] is a bit like the previous mathematical interval, the right side is the open interval, [1:3] is [1,3] is 1,2.

tuples

A tuple is a special list that cannot be changed after it is declared and can be declared by ().

names=('java'.'python')
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The dictionary

Lists are ordered and elements are accessed by position, whereas dictionaries are unordered and elements are stored and accessed by key-value pairs. Dictionaries can be declared with {}.

D = {}
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Dictionaries can be nested

D ={'food': {'egg': 1, 'ham': 2}}
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Dictionaries can retrieve keys, values, and key + values by keys, values, and items.

D = {'egg': 1, 'ham'2} :print(D.keys())
print(D.values())
print(D.items())
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Get to get the value of a key by key.

D = {'egg': 1, 'ham'2} :print(D.get('egg'))
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Add or change dictionaries by keys

D = {'egg': 1, 'ham'2} :D['egg'] = 2
print(D)
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Delete elements by del and POP

D = {'egg': 1, 'ham'2} :del D['egg']
D.pop('ham')
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Merge two dictionaries via update

D1 = {'bread': 3}
D = {'egg': 1, 'ham'2} :D.update(D1)
print(D)
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Get the dictionary length by len

D = {'egg': 1, 'ham'2} :print(len(D))
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The last

This is a very simple introduction to Python data structures, but it’s best to type them yourself. More articles can be found on QStack.

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