翻译:《实用的Python编程》08_02_Logging
2021-04-10 22:55
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8.2 日志
本节对日志模块(logging module)进行简单的介绍。
logging 模块
logging模块是用于记录诊断信息的 Python 标准库模块。日志模块非常庞大,具有许多复杂的功能。我们将会展示一个简单的例子来说明其用处。
再探异常
在本节练习中,我们创建这样一个
parse()函数:
# fileparse.py def parse(f, types=None, names=None, delimiter=None): records = [] for line in f: line = line.strip() if not line: continue try: records.append(split(line,types,names,delimiter)) except ValueError as e: print("Couldn't parse :", line) print("Reason :", e)return records
请看到
try-except语句,在
except块中,我们应该做什么?
应该打印警告消息(warning message)?
try: records.append(split(line,types,names,delimiter)) except ValueError as e: print("Couldn't parse :", line) print("Reason :", e)
还是默默忽略警告消息?
try: records.append(split(line,types,names,delimiter)) except ValueError as e: pass
任何一种方式都无法令人满意,通常情况下,两种方式我们都需要(用户可选)。
使用 logging
logging模块可以解决这个问题:
# fileparse.py import logging log = logging.getLogger(__name__) def parse(f,types=None,names=None,delimiter=None): ... try: records.append(split(line,types,names,delimiter)) except ValueError as e: log.warning("Couldn't parse : %s", line) log.debug("Reason : %s", e)
修改代码以使程序能够遇到问题的时候发出警告消息,或者特殊的
Logger对象。
Logger对象使用
logging.getLogger(__name__)创建。
日志基础
创建一个记录器对象(logger object)。
log = logging.getLogger(name) # name is a string
发出日志消息:
log.critical(message [, args]) log.error(message [, args]) log.warning(message [, args]) log.info(message [, args]) log.debug(message [, args])
不同方法代表不同级别的严重性。
所有的方法都创建格式化的日志消息。
args和
%运算符 一起使用以创建消息。
logmsg = message % args # Written to the log
日志配置
配置:
# main.py ... if __name__ == '__main__': import logging logging.basicConfig( filename = 'app.log', # Log output file level = logging.INFO, # Output level )
通常,在程序启动时,日志配置是一次性的(译注:程序启动后无法重新配置)。该配置与日志调用是分开的。
说明
日志是可以任意配置的。你可以对日志配置的任何一方面进行调整:如输出文件,级别,消息格式等等,不必担心对使用日志模块的代码造成影响。
练习
练习 8.2:将日志添加到模块中
在
fileparse.py中,有一些与异常有关的错误处理,这些异常是由错误输入引起的。如下所示:
# fileparse.py import csv def parse_csv(lines, select=None, types=None, has_headers=True, delimiter=',', silence_errors=False): ''' Parse a CSV file into a list of records with type conversion. ''' if select and not has_headers: raise RuntimeError('select requires column headers') rows = csv.reader(lines, delimiter=delimiter) # Read the file headers (if any) headers = next(rows) if has_headers else [] # If specific columns have been selected, make indices for 56c filtering and set output columns if select: indices = [ headers.index(colname) for colname in select ] headers = select records = [] for rowno, row in enumerate(rows, 1): if not row: # Skip rows with no data continue # If specific column indices are selected, pick them out if select: row = [ row[index] for index in indices] # Apply type conversion to the row if types: try: row = [func(val) for func, val in zip(types, row)] except ValueError as e: if not silence_errors: print(f"Row {rowno}: Couldn't convert {row}") print(f"Row {rowno}: Reason {e}") continue # Make a dictionary or a tuple if headers: record = dict(zip(headers, row)) else: record = tuple(row) records.append(record) return records
请注意发出诊断消息的
# fileparse.py import csv import logging log = logging.getLogger(__name__) def parse_csv(lines, select=None, types=None, has_headers=True, delimiter=',', silence_errors=False): ad8 ''' Parse a CSV file into a list of records with type conversion. ''' if select and not has_headers: raise RuntimeError('select requires column headers') rows = csv.reader(lines, delimiter=delimiter) # Read the file headers (if any) headers = next(rows) if has_headers else [] # If specific columns have been selected, make indices for filtering and set output columns if select: indices = [ headers.index(colname) for colname in select ] headers = select records = [] for rowno, row in enumerate(rows, 1): if not row: # Skip rows with no data continue # If specific column indices are selected, pick them out if select: row = [ row[index] for index in indices] # Apply type conversion to the row if types: try: row = [func(val) for func, val in zip(types, row)] except ValueError as e: if not silence_errors: log.warning("Row %d: Couldn't convert %s", rowno, row) log.debug("Row %d: Reason %s", rowno, e) continue # Make a dictionary or a tuple if headers: record = dict(zip(headers, row)) else: record = tuple(row) records.append(record) return records
完成修改后,尝试在错误的数据上使用这些代码:
>>> import report >>> a = report.read_portfolio('Data/missing.csv') Row 4: Bad row: ['MSFT', '', '51.23'] Row 7: Bad row: ['IBM', '', '70.44'] >>>
如果你什么都不做,则只会获得
WARNING级别以上的日志消息。输出看起来像简单的打印语句。但是,如果你配置了日志模块,你将会获得有关日志级别,模块等其它信息。请按以下步骤操作查看:
>>> import logging >>> logging.basicConfig() >>> a = report.read_portfolio('Data/missing.csv') WARNING:fileparse:Row 4: Bad row: ['MSFT', '', '51.23'] WARNING:fileparse:Row 7: Bad row: ['IBM', '', '70.44'] >>>
你会发现,看不到来自于
log.debug()操作的输出。请按以下步骤修改日志级别(译注:因为日志配置是一次性的,所以该操作需要重启命令行窗口):
>>> logging.getLogger('fileparse').level = logging.DEBUG >>> a = report.read_portfolio('Data/missing.csv') WARNING:fileparse:Row 4: Bad row: ['MSFT', '', '51.23'] DEBUG:fileparse:Row 4: Reason: invalid literal for int() with base 10: '' WARNING:fileparse:Row 7: Bad row: ['IB 564 M', '', '70.44'] DEBUG:fileparse:Row 7: Reason: invalid literal for int() with base 10: '' >>>
只留下 critical 级别的日志消息,关闭其它级别的日志消息。
>>> logging.getLogger('fileparse').level=logging.CRITICAL >>> a = report.read_portfolio('Data/missing.csv') >>>
练习 8.3:向程序添加日志
要添加日志到应用中,你需要某种机制来实现在主模块中初始化日志。其中一种方式使用看起来像下面这样的代码:
# This file sets up basic configuration of the logging module. # Change settings here to adjust logging output as needed. import logging logging.basicConfig( filename = 'app.log', # Name of the log file (omit to use stderr) filemode = 'w', # File mode (use 'a' to append) level = logging.WARNING, # Logging level (DEBUG, INFO, WARNING, ERROR, or CRITICAL) )
再次说明,你需要将日志配置代码放到程序启动步骤中。例如,将其放到
report.py程序里的什么位置?
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