File name is the same as the package name to be referenced

For example, if you want to reference requests, but name your own file also called requests.py, execute the following code

import requests
requests.get('http://www.baidu.com')
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The following error will be reported

AttributeError: module 'requests' has no attribute 'get'
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The solution is to give your python file a different name, as long as it's not the same as the package name. If you really don't want to change the file name, you can use the following method

import sys
_cpath_ = sys.path[0]
print(sys.path)
print(_cpath_)
sys.path.remove(_cpath_)
import requests
sys.path.insert(0, _cpath_)

requests.get('http://www.baidu.com')
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The main principle is to exclude the current directory from the lookup directory where python is running. Executing python requests.py on the command line after this process works fine, but debugging and running in pycharm is not possible.

Misaligned formatting

Here's a piece of normal code

def fun():
    a=1
    b=2
    if a>b:
        print("a")  
    else:
        print("b")

fun()
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1. If else is not aligned

def fun():
    a=1
    b=2
    if a>b:
        print("a")  
     else:
        print("b")

fun()
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Will report

IndentationError: unindent does not match any outer indentation level
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2. If else and if do not appear in pairs, such as writing an else directly or an extra else, or if and the colon following the else are omitted

def fun():
    a=1
    b=2
    else:
        print("b")

fun()
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def fun():
    a=1
    b=2
    if a>b:
        print("a")
    else:
        print("b")
    else:
        print("b")

fun()
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def fun():
    a=1
    b=2
    if a>b:
        print("a")
    else
        print("b")

fun()
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Metropolitan newspaper

SyntaxError: invalid syntax
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3. If the statement below if and else is not indented

def fun():
    a=1
    b=2
    if a>b:
    print("a")
    else:
    print("b")

fun()
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Will report

IndentationError: expected an indented block
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Use quotation marks in Chinese for Strings

For example, use Chinese quotation marks below

print("a")
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Will report

SyntaxError: invalid character in identifier
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The correct way is to use single or double quotation marks in English

print('b')
print("b")
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No call to function, mistaken for function not to execute

For example, the following code

class A(object):
    def run(self):
        print('run')

a = A()
a.run
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The program is normal and runs without errors, but it may be curious why there is no printout, of course, because a.run returns a reference to a function that is not executed and a is called. Run() will find the printout. If you change the code, change to

class A(object):
    def run(self):
        return 1

a = A()
print(a.run+1)
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You will see the error

TypeError: unsupported operand type(s) for +: 'method' and 'int'
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Changing to a.run()+1 will work.

String Formatting

This is a normal procedure

a = 1
b = 2
print('a = %s'%a)
print('a,b = %s,%s'%(a,b))
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1. If you write less%s

a = 1
b = 2
print('a = '%a) # error
print('a,b = %s'%(a,b)) # error
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Meeting Report

TypeError: not all arguments converted during string formatting
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2. If you write more%s

a = 1
b = 2
print('a = %s,%s'%a)
print('a,b = %s,%s,%s'%(a,b))
``
Meeting Report
```bash
TypeError: not enough arguments for format string
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3. If the formatted string is incorrect, such as s in uppercase

a = 1
b = 2
print('a = %S'%a)
print('a,b = %S,%S'%(a,b))
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Meeting Report

ValueError: unsupported format character 'S' (0x53) at index 5
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4. If nothing is written behind%

a = 1
b = 2
print('a = %'%a)
print('a,b = %,%'%(a,b))
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Meeting Report

ValueError: incomplete format
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Error on None operation

Like this code

a = [3,2,1]
b = a.sort()
print(a)
print(b)
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The sorted value is [1,2,3], and the return value of the sort function is None, so the value of b is actually None, not [1,2,3].

If this is the time to manipulate b, such as taking the first element of B

print(b[0])
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Error will occur

TypeError: 'NoneType' object is not subscriptable
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Such as copying arrays

print(b*2)
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Error will occur

TypeError: unsupported operand type(s) for *: 'NoneType' and 'int'
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For example, execute the extend function

b.extend([4])
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Error will occur

AttributeError: 'NoneType' object has no attribute 'extend'
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Integer Division

The default integer division in python2 returns the integer part

print(3/2)
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Return 1 and return decimal in python3

print(3/2)
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Return is 1.5 so the following code

a = [1,2,3]
print(a[len(a)/2])
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You get a value of 2 in python2, and you do get an error executing in python3

TypeError: list indices must be integers or slices, not float
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There are two ways to modify this. 1. Turn the result into an integer

a = [1,2,3]
print(a[int(len(a)/2)])
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2. Use //

a = [1,2,3]
print(a[len(a)//2])
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Both are also appropriate for python2, so when expecting integers to return, it is advisable to use a double division sign to express your intentions explicitly

Primary key does not exist

The acquired build dictionary does not exist

a = {'A':1}
print(a['a'])
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Errors will occur

KeyError: 'a'
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Network timeout during pip installation

Similar to the following error bash WARNING: Retrying (total=3, connect=None, read=None, redirect=None, status=None)) after connection break by'ConnectTimeoutError (<pip. _vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7f3b6ea319b0>,'Connection to files.pythonhosted.org timed. (connect timeout=15)'): /xpackages/xxxxxx Recommends setting up a mirror source, such as Tsinghua source, for reference Portal

You may also encounter the following error without adding the trusted-host parameter

Collecting xxx
The repository located at pypi.tuna.tsinghua.edu.cn is not a trusted or secure host and is being ignored. If this repository is available via HTTPS it is recommended to use HTTPS instead, otherwise you may silence this warning and allow it anyways with '--trusted-host pypi.tuna.tsinghua.edu.cn'.
Could not find a version that satisfies the requirement xxx (from versions: )
No matching distribution found for xxx
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Installation command added--trust-host PIP install-i pypi.tuna.tsinghua.edu.cn/simple --trusted-host pypi.tuna.tsinghua.edu.cn xxx

Author: Ice wind in the sky
Links: https://juejin.cn/post/7023700981665759240
Source: Rare Earth Excavation
Copyright belongs to the author. For commercial reprinting, please contact the author for authorization. For non-commercial reprinting, please indicate the source.