Another alternative is to use a lambda:
ent.bind("<Return>", (lambda event: name_of_function()))
Full code:
from tkinter import *
from tkinter.messagebox import showinfo
def reply(name):
showinfo(title="Reply", message = "Hello %s!" % name)
top = Tk()
top.title("Echo")
top.iconbitmap("Iconshock-Folder-Gallery.ico")
Label(top, text="Enter your name:").pack(side=TOP)
ent = Entry(top)
ent.bind("<Return>", (lambda event: reply(ent.get())))
ent.pack(side=TOP)
btn = Button(top,text="Submit", command=(lambda: reply(ent.get())))
btn.pack(side=LEFT)
top.mainloop()
As you can see, creating a lambda function with an unused variable "event" solves the problem.