为什么我得到“NameError：名称'数据库'未定义”，即使我正在定义主？

Question

当我尝试运行我的代码时，出现名称错误：

Traceback (most recent call last):
  File "dna.py", line 24, in <module>
    main ()
  File "dna.py", line 15, in main
    STR_searcher()
  File "dna.py", line 19, in STR_searcher
    STR_dict = dict.fromkeys(range(1, len(database.fieldnames)))
NameError: name 'database' is not defined

当我将辅助函数放在顶部时，程序可以运行，但我计划使用更多函数，因此我想将它们放在底部并将第一个定义为 main。我也尝试过使用if __name__ == "__main__": main()，但这也没有用。那么如何在确保定义所有内容的同时将其他函数放在 main 之下？

from sys import argv, exit
import csv
from collections import OrderedDict

def main():
    if len(argv) != 3:
        print("Usage: python dna.py data.csv sequence.txt")
        exit(1)
    
with open(argv[1]) as csv_file: 
    database = csv.DictReader(csv_file)

    with open(argv[2]) as txt_file: 
        sequence = txt_file.read()
        STR_searcher()
                    
        
def STR_searcher():
    STR_dict = dict.fromkeys(range(1, len(database.fieldnames)))
    for i in range(len(STR_dict)):
        for j in range(len(sequence)):
            print("hello")        
            
main ()

Answer 1

这是因为在STR_searcher()的函数范围内没有定义变量database。要将变量赋予函数，将其定义为： def STR_searcher(database): 并从 main 函数中调用它，例如 STR_searcher(database)。

Answer 2

发生这种情况是因为您的 database 变量是在您的 main 函数的上下文中定义的，而在 STR_searcher 内部它就好像它不存在一样。考虑将其移至一个类，例如：

def MyClass(object):
    def __init__(self):
        self.database =None
        self.sequence=None
    
    def main(self):
        if len(argv) != 3:
            print("Usage: python dna.py data.csv sequence.txt")
            exit(1)
            
        with open(argv[1]) as csv_file: 
            self.database = csv.DictReader(csv_file)
        
            with open(argv[2]) as txt_file: 
                self.sequence = txt_file.read()
                self.STR_searcher()
                        
            
    def STR_searcher(self):
        STR_dict = dict.fromkeys(range(1, len(self.database.fieldnames)))
        for i in range(len(STR_dict)):
            for j in range(len(self.sequence)):
                print("hello")    

然后您可以通过以下方式运行它：

Myclass().main()

Answer 3

你应该将变量传递给函数

from collections import OrderedDict
from sys import argv, exit
import csv

def main():
    if len(argv) != 3:
        print("Usage: python dna.py data.csv sequence.txt")
        exit(1)

    with open(argv[1]) as csv_file: 
        database = csv.DictReader(csv_file)

    with open(argv[2]) as txt_file: 
        sequence = txt_file.read()
    
    STR_searcher(database, sequence)
        
def STR_searcher(database, sequence):
    STR_dict = dict.fromkeys(range(1, len(database.fieldnames)))
    for i in range(len(STR_dict)):
        for j in range(len(sequence)):
            print("hello")        
            
if __name__ == "__main__":
    main()

或者您可以使用 global 关键字，但这不是一个好方法。

from collections import OrderedDict
from sys import argv, exit
import csv

database = None
sequence = None

def main():
    global database
    global sequence

    if len(argv) != 3:
        print("Usage: python dna.py data.csv sequence.txt")
        exit(1)

    with open(argv[1]) as csv_file: 
        database = csv.DictReader(csv_file)

    with open(argv[2]) as txt_file: 
        sequence = txt_file.read()
    
    STR_searcher()
           
def STR_searcher():
    global database
    global sequence
    
    STR_dict = dict.fromkeys(range(1, len(database.fieldnames)))
    for i in range(len(STR_dict)):
        for j in range(len(sequence)):
            print("hello")        
            
if __name__ == "__main__":
    main()