>我正在处理一个同时抛出错误和警告的函数。(相关:关于警告的警告)
通常,警告会继续错误。在这些情况下,我想忽略警告,只处理错误。
另一方面,如果只有一个警告(没有错误),那么我想捕捉警告。
我正在尝试使用臭名昭著的易于使用的tryCatch
。
我的直接问题是:有没有办法强制tryCatch
在warning
之前处理error
(或在出现错误时忽略警告)?
我从?tryCatch
文档中的理解是,条件是处理FIFO的,在这种情况下,我的直接问题的答案是否定的 - 至少不是直接的。 在这种情况下,是否可以处理警告,然后让函数继续,同时仍然捕获错误?
我无法使用的解决方案:
-
suppressWarnings
# 我仍然想捕获并处理警告 -
options(warn=2)
# 某些警告是无害的
relevant from `?tryCatch`
如果在评估 expr 时发出条件信号,则会检查已建立的处理程序,从最近建立的处理程序开始,以查找与条件类匹配的处理程序。当在单个 tryCatch 中提供多个处理程序时,第一个处理程序被认为比第二个处理程序更新。如果找到处理程序,则控制权将转移到建立处理程序的 tryCatch 调用,找到处理程序并取消建立所有更新的处理程序,使用条件作为其参数调用处理程序,并且处理程序返回的结果作为 tryCatch 调用的值返回。
下面是一个玩具示例:
F.errorAndWarning <- function() {
warning("Warning before the error")
cat("I have moved on.")
stop("error")
TRUE
}
F.error <- function() {stop("error"); TRUE}
test <- function(F)
tryCatch(expr= {F}()
, error=function(e) cat("ERROR CAUGHT")
, warning=function(w) cat("WARNING CAUGHT")
)
test(F.error)
# ERROR CAUGHT
test(F.errorAndWarning)
# WARNING CAUGHT
预期/理想输出:
test(F.errorAndWarning)
# ERROR CAUGHT
"是否可以处理警告,然后让函数继续,同时仍然捕获错误?"问题有关。
我有一个类似的问题,我想将警告和错误的日志记录函数绑定到 try catch,并在发出警告后始终继续,并且还能够对 try catch 执行多次尝试,例如访问脆弱的网络驱动器。这就是我最终使用的。这个或更简化的版本可以帮助您了解您的追求。
MyLibrary.Sys.Try <- function(
expr, # Expression that will be evaluated by the call to Try
errorMessage="", # Optional prepended string to add to error output
warningMessage="", # Optional prepended string to add to warning output
failureMessage="", # Optional prepended string to add to failing all attempts
finally=NULL, # Optional expression to be executed at the end of tryCatch
attempts=1, # Number of attempts to try evaluating the expression
suppressError=TRUE, # Should the call just log the error or raise it if all attempts fail
quiet=FALSE # Return expression normally or as invisible
) {
tryNumber <- 0
while(tryNumber<attempts) {
tryNumber <- tryNumber + 1
# If not suppressing the error and this is the last
# attempt then just evaluate the expression straight out
if(tryNumber == attempts && !suppressError){
# NOTE: I think some warnings might be lost here when
# running in non-interactive mode. But I think it should be okay
# because even nested dispatch seems to pick them up:
# MyLibrary.Sys.Try(MyLibrary.Sys.Try(function(),suppressError=F))
return(expr)
}
tryCatch({
# Set the warning handler to an empty function
# so it won't be raised by tryCatch but will
# be executed by withCallingHandlers
options(warning.expression=quote(function(){}))
withCallingHandlers({
if(quiet) {
return(invisible(expr))
} else {
return(expr)
}
},error=function(ex){
MyLibrary.Sys.Log.Error(errorMessage,ex)
}, warning=function(warn){
# Had issues with identical warning messages being
# issued here so to avoid that only log it the first
# time it happens in a given minute.
warnStamp <- paste(Sys.time(),warn,collapse="_",sep="")
if(!identical(warnStamp,getOption("MyLibrary.LAST.WARNING"))) {
if(!(interactive() && is.null(getOption("warning.expression")))){
MyLibrary.Sys.Log.Warning(warningMessage,warn)
}
options(MyLibrary.LAST.WARNING=warnStamp)
}
})
},error=function(ex){
# Suppressing the error since it's been logged
# by the handler above. Needs to be suppressed
# to not invoke the stop directly since the
# handler above passes it through.
},finally={
# Set the warning handler to the default value
# of NULL which will cause it to revert to it's
# normal behaviour. If a custom handler is normally
# attached it would make sense to store it above
# and then restore it here. But don't need that now
options(warning.expression=NULL)
if(!is.null(finally)){
if(quiet) {
return(invisible(finally))
} else {
return(finally)
}
}
})
}
msg <- paste(ifelse(nchar(failureMessage)>0," - ",""),"Failed to call expression after ",attempts," attempt(s)",sep="")
MyLibrary.Sys.Log.Error(failureMessage,msg)
}
我会编写一个执行expression
并确定错误优先级的函数。
prioritize.errors <- local({
# this function executes an expression and stores the warnings
# until it finishes executing.
warnings <- list()
w.handler <- function(w) {
warnings <<- c(warnings, list(w))
invokeRestart('muffleWarning') # here's the trick
}
function(expr) {
withCallingHandlers({expr}, warning=w.handler)
for (w in warnings) warning(w)
warnings <<- list()
}
})
F.warning <- function() {
warning("a warning")
message('ok')
}
test <- function(expr) {
tryCatch(expr,
error=function(e) cat("ERROR CAUGHT"),
warning=function(w) cat("WARNING CAUGHT")
)
}
test(prioritize.errors(F.error()))
# ERROR CAUGHT
test(prioritize.errors(F.warning()))
# ok
# WARNING CAUGHT
test(prioritize.errors(F.errorAndWarning()))
# I have moved on.ERROR CAUGHT
我在 pander 包中编写了一个方便的帮助程序函数用于评估,它捕获所有警告、错误和标准输出上打印的任何内容,以及调用中返回的原始 R 对象:
> library(pander)
> evals('F.errorAndWarning()')
[[1]]
$src
[1] "F.errorAndWarning()"
$result
NULL
$output
NULL
$type
[1] "error"
$msg
$msg$messages
NULL
$msg$warnings
[1] "Warning before the error"
$msg$errors
[1] "error"
$stdout
[1] "I have moved on."
attr(,"class")
[1] "evals"
这三个答案都非常广泛和不错的工作,但我认为很多人也在寻找一种简短、简单的方法来处理警告,但要继续执行。正如Matthew所展示的那样,这可以很快完成:通过调用重新启动(并使用withCallingHandlers):
test <- function(FUN) withCallingHandlers(
expr=FUN(),
error=function(e) cat("ERROR CAUGHTn"),
warning=function(w) {cat('WARNING CAUGHTn'); invokeRestart(findRestart('muffleWarning'))}
)
这仍会打印警告(即使稍后生成错误),但会继续执行